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    /*
 * Copyright (c) 2017, Haiyang Li.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.landawn.abacus.util;

import java.math.BigDecimal;
import java.math.BigInteger;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Comparator;
import java.util.Deque;
import java.util.HashMap;
import java.util.HashSet;
import java.util.IdentityHashMap;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.NavigableMap;
import java.util.NavigableSet;
import java.util.PriorityQueue;
import java.util.Queue;
import java.util.Set;
import java.util.SortedMap;
import java.util.SortedSet;
import java.util.TreeMap;
import java.util.TreeSet;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.regex.Pattern;

import com.landawn.abacus.annotation.Beta;
import com.landawn.abacus.util.Tuple.Tuple1;
import com.landawn.abacus.util.Tuple.Tuple2;
import com.landawn.abacus.util.Tuple.Tuple3;
import com.landawn.abacus.util.Tuple.Tuple4;
import com.landawn.abacus.util.function.BiConsumer;
import com.landawn.abacus.util.function.BiFunction;
import com.landawn.abacus.util.function.BiPredicate;
import com.landawn.abacus.util.function.BinaryOperator;
import com.landawn.abacus.util.function.BooleanSupplier;
import com.landawn.abacus.util.function.Consumer;
import com.landawn.abacus.util.function.DoubleBiPredicate;
import com.landawn.abacus.util.function.DoublePredicate;
import com.landawn.abacus.util.function.Function;
import com.landawn.abacus.util.function.IndexedBiConsumer;
import com.landawn.abacus.util.function.IndexedBiFunction;
import com.landawn.abacus.util.function.IndexedBiPredicate;
import com.landawn.abacus.util.function.IndexedConsumer;
import com.landawn.abacus.util.function.IndexedFunction;
import com.landawn.abacus.util.function.IndexedPredicate;
import com.landawn.abacus.util.function.IntBiPredicate;
import com.landawn.abacus.util.function.IntFunction;
import com.landawn.abacus.util.function.IntPredicate;
import com.landawn.abacus.util.function.LongBiPredicate;
import com.landawn.abacus.util.function.LongPredicate;
import com.landawn.abacus.util.function.Predicate;
import com.landawn.abacus.util.function.QuadFunction;
import com.landawn.abacus.util.function.Supplier;
import com.landawn.abacus.util.function.ToByteFunction;
import com.landawn.abacus.util.function.ToCharFunction;
import com.landawn.abacus.util.function.ToDoubleFunction;
import com.landawn.abacus.util.function.ToFloatFunction;
import com.landawn.abacus.util.function.ToIntFunction;
import com.landawn.abacus.util.function.ToLongFunction;
import com.landawn.abacus.util.function.ToShortFunction;
import com.landawn.abacus.util.function.TriConsumer;
import com.landawn.abacus.util.function.TriFunction;
import com.landawn.abacus.util.function.TriPredicate;
import com.landawn.abacus.util.function.UnaryOperator;
import com.landawn.abacus.util.stream.Collector;
import com.landawn.abacus.util.stream.Collectors;
import com.landawn.abacus.util.stream.Stream;

/**
 * Factory utility class for functional interfaces.
 * 
 * 
     * 
 * 
 * Map map = N.asMap("a", 1, "b", 2, "c", 3);
 * // Instead of
 * Stream.of(map).filter(e -> e.getKey().equals("a") || e.getKey().equals("b")).toMap(e -> e.getKey(), e -> e.getValue());
 * // Using Fn
 * Stream.of(map).filter(Fn.testByKey(k -> k.equals("a") || k.equals("b"))).collect(Collectors.toMap());
 * 
 * 
 * 
    
 * 
 * 
 * @author haiyang li
 *
 */
public final class Fn extends Comparators {

    @SuppressWarnings("rawtypes")
    public static final IntFunction> FACTORY_OF_MAP = (IntFunction) Factory.MAP_FACTORY;
    @SuppressWarnings("rawtypes")
    public static final IntFunction> FACTORY_OF_LINKED_HASH_MAP = (IntFunction) Factory.LINKED_HASH_MAP_FACTORY;
    @SuppressWarnings("rawtypes")
    public static final Supplier> SUPPLIER_OF_MAP = (Supplier) Suppliers.MAP;
    @SuppressWarnings("rawtypes")
    public static final Supplier> SUPPLIER_OF_LINKED_HASH_MAP = (Supplier) Suppliers.LINKED_HASH_MAP;

    private static final com.landawn.abacus.util.function.Runnable EMPTY_ACTION = new com.landawn.abacus.util.function.Runnable() {
        @Override
        public void run() {
        }
    };

    @SuppressWarnings("rawtypes")
    private static final Consumer DO_NOTHING = new Consumer() {
        @Override
        public void accept(Object value) {
            // do nothing.
        }
    };

    private static final Consumer CLOSE = new Consumer() {
        @Override
        public void accept(AutoCloseable value) {
            IOUtil.close(value);
        }
    };

    private static final Consumer CLOSE_QUIETLY = new Consumer() {
        @Override
        public void accept(AutoCloseable value) {
            IOUtil.closeQuietly(value);
        }
    };

    @SuppressWarnings("rawtypes")
    private static final BiConsumer PRINTLN_EQUAL = new BiConsumer() {
        @Override
        public void accept(Object key, Object value) {
            N.println(StringUtil.concat(N.toString(key), "=", N.toString(value)));
        }
    };

    @SuppressWarnings("rawtypes")
    private static final BiConsumer PRINTLN_HYPHEN = new BiConsumer() {
        @Override
        public void accept(Object key, Object value) {
            N.println(StringUtil.concat(N.toString(key), "-", N.toString(value)));
        }
    };

    @SuppressWarnings("rawtypes")
    private static final BiConsumer PRINTLN_UNDERSCORE = new BiConsumer() {
        @Override
        public void accept(Object key, Object value) {
            N.println(StringUtil.concat(N.toString(key), "_", N.toString(value)));
        }
    };

    @SuppressWarnings("rawtypes")
    private static final BiConsumer PRINTLN_COLON = new BiConsumer() {
        @Override
        public void accept(Object key, Object value) {
            N.println(StringUtil.concat(N.toString(key), ":", N.toString(value)));
        }
    };

    @SuppressWarnings("rawtypes")
    private static final BiConsumer PRINTLN_COLON_SPACE = new BiConsumer() {
        @Override
        public void accept(Object key, Object value) {
            N.println(StringUtil.concat(N.toString(key), ": ", N.toString(value)));
        }
    };

    @SuppressWarnings("rawtypes")
    private static final BiConsumer PRINTLN_COMMA = new BiConsumer() {
        @Override
        public void accept(Object key, Object value) {
            N.println(StringUtil.concat(N.toString(key), ",", N.toString(value)));
        }
    };

    @SuppressWarnings("rawtypes")
    private static final BiConsumer PRINTLN_COMMA_SPACE = new BiConsumer() {
        @Override
        public void accept(Object key, Object value) {
            N.println(StringUtil.concat(N.toString(key), ", ", N.toString(value)));
        }
    };

    @SuppressWarnings("rawtypes")
    private static final BiConsumer PRINTLN_EMPTY = new BiConsumer() {
        @Override
        public void accept(Object key, Object value) {
            N.println(StringUtil.concat(N.toString(key), N.toString(value)));
        }
    };

    @SuppressWarnings("rawtypes")
    private static final Consumer PRINTLN = new Consumer() {
        @Override
        public void accept(Object value) {
            N.println(value);
        }
    };

    @SuppressWarnings("rawtypes")
    private static final Function TO_STRING = new Function() {
        @Override
        public Object apply(Object t) {
            return N.toString(t);
        }
    };

    private static final Function TO_CAMEL_CASE = new Function() {
        @Override
        public String apply(String t) {
            return StringUtil.toCamelCase(t);
        }
    };

    private static final Function TO_LOWER_CASE = new Function() {
        @Override
        public String apply(String t) {
            return StringUtil.toLowerCase(t);
        }
    };

    private static final Function TO_LOWER_CASE_WITH_UNDERSCORE = new Function() {
        @Override
        public String apply(String t) {
            return StringUtil.toLowerCaseWithUnderscore(t);
        }
    };

    private static final Function TO_UPPER_CASE = new Function() {
        @Override
        public String apply(String t) {
            return StringUtil.toUpperCase(t);
        }
    };

    private static final Function TO_UPPER_CASE_WITH_UNDERSCORE = new Function() {
        @Override
        public String apply(String t) {
            return StringUtil.toUpperCaseWithUnderscore(t);
        }
    };

    @SuppressWarnings("rawtypes")
    private static final BiFunction COMPARE = new BiFunction() {
        @Override
        public Integer apply(Comparable a, Comparable b) {
            return N.compare(a, b);
        }
    };

    @SuppressWarnings("rawtypes")
    private static final Function IDENTITY = new Function() {
        @Override
        public Object apply(Object t) {
            return t;
        }
    };

    private static final Function TRIM = new Function() {
        @Override
        public String apply(String t) {
            return t == null ? null : t.trim();
        }
    };

    private static final Function TRIM_TO_EMPTY = new Function() {
        @Override
        public String apply(String t) {
            return t == null ? "" : t.trim();
        }
    };

    private static final Function TRIM_TO_NULL = new Function() {
        @Override
        public String apply(String t) {
            if (t == null || (t = t.trim()).length() == 0) {
                return null;
            }

            return t;
        }
    };

    private static final Function NULL_TO_EMPTY = new Function() {
        @Override
        public String apply(String t) {
            return t == null ? N.EMPTY_STRING : t;
        }
    };

    @SuppressWarnings("rawtypes")
    private static final Function NULL_TO_EMPTY_L = new Function() {
        @Override
        public List apply(List t) {
            return t == null ? N.emptyList() : t;
        }
    };

    @SuppressWarnings("rawtypes")
    private static final Function NULL_TO_EMPTY_S = new Function() {
        @Override
        public Set apply(Set t) {
            return t == null ? N.emptySet() : t;
        }
    };

    @SuppressWarnings("rawtypes")
    private static final Function NULL_TO_EMPTY_M = new Function() {
        @Override
        public Map apply(Map t) {
            return t == null ? N.emptyMap() : t;
        }
    };

    private static final Function LENGTH = new Function() {
        @Override
        public Integer apply(String t) {
            return N.len(t);
        }
    };

    @SuppressWarnings("rawtypes")
    private static final Function SIZE = new Function() {
        @Override
        public Integer apply(Collection t) {
            return N.len(t);
        }
    };

    private static final Function, Object> KEY = new Function, Object>() {
        @Override
        public Object apply(Map.Entry t) {
            return t.getKey();
        }
    };

    private static final Function, Object> VALUE = new Function, Object>() {
        @Override
        public Object apply(Map.Entry t) {
            return t.getValue();
        }
    };

    private static final Function, Map.Entry> INVERSE = new Function, Map.Entry>() {
        @Override
        public Map.Entry apply(Map.Entry t) {
            return Pair.of(t.getValue(), t.getKey());
        }
    };

    //    private static final BiFunction> ENTRY = new BiFunction>() {
    //        @Override
    //        public Map.Entry apply(Object key, Object value) {
    //            return new AbstractMap.SimpleImmutableEntry<>(key, value);
    //        }
    //    };

    private static final BiFunction> PAIR = new BiFunction>() {
        @Override
        public Pair apply(Object key, Object value) {
            return Pair.of(key, value);
        }
    };

    private static final TriFunction> TRIPLE = new TriFunction>() {
        @Override
        public Triple apply(Object a, Object b, Object c) {
            return Triple.of(a, b, c);
        }
    };

    private static final Function> TUPLE_1 = new Function>() {
        @Override
        public Tuple1 apply(Object t) {
            return Tuple.of(t);
        }
    };

    private static final BiFunction> TUPLE_2 = new BiFunction>() {
        @Override
        public Tuple2 apply(Object t, Object u) {
            return Tuple.of(t, u);
        }
    };

    private static final TriFunction> TUPLE_3 = new TriFunction>() {
        @Override
        public Tuple3 apply(Object a, Object b, Object c) {
            return Tuple.of(a, b, c);
        }
    };

    private static final QuadFunction> TUPLE_4 = new QuadFunction>() {
        @Override
        public Tuple4 apply(Object a, Object b, Object c, Object d) {
            return Tuple.of(a, b, c, d);
        }
    };

    @SuppressWarnings("rawtypes")
    private static final Predicate ALWAYS_TRUE = new Predicate() {
        @Override
        public boolean test(Object value) {
            return true;
        }
    };

    @SuppressWarnings("rawtypes")
    private static final Predicate ALWAYS_FALSE = new Predicate() {
        @Override
        public boolean test(Object value) {
            return false;
        }
    };

    @SuppressWarnings("rawtypes")
    private static final Predicate IS_NULL = new Predicate() {
        @Override
        public boolean test(Object value) {
            return value == null;
        }
    };

    private static final Predicate IS_NULL_OR_EMPTY = new Predicate() {
        @Override
        public boolean test(CharSequence value) {
            return value == null || value.length() == 0;
        }
    };

    private static final Predicate IS_NULL_OR_EMPTY_OR_BLANK = new Predicate() {
        @Override
        public boolean test(CharSequence value) {
            return N.isNullOrEmptyOrBlank(value);
        }
    };

    @SuppressWarnings("rawtypes")
    private static final Predicate NOT_NULL = new Predicate() {
        @Override
        public boolean test(Object value) {
            return value != null;
        }
    };

    private static final Predicate NOT_NULL_OR_EMPTY = new Predicate() {
        @Override
        public boolean test(CharSequence value) {
            return value != null && value.length() > 0;
        }
    };

    private static final Predicate NOT_NULL_OR_EMPTY_OR_BLANK = new Predicate() {
        @Override
        public boolean test(CharSequence value) {
            return N.notNullOrEmptyOrBlank(value);
        }
    };

    private static final ToIntFunction NUM_TO_INT_FUNC = new ToIntFunction() {
        @Override
        public int applyAsInt(Number value) {
            return value == null ? 0 : value.intValue();
        }
    };

    private static final ToLongFunction NUM_TO_LONG_FUNC = new ToLongFunction() {
        @Override
        public long applyAsLong(Number value) {
            return value == null ? 0 : value.longValue();
        }
    };

    private static final ToDoubleFunction NUM_TO_DOUBLE_FUNC = new ToDoubleFunction() {
        @Override
        public double applyAsDouble(Number value) {
            return value == null ? 0d : value.doubleValue();
        }
    };

    private static final Object NULL = new Object();

    private Fn() {
        super();
        // Singleton.
    }

    public static  T get(final Supplier supplier) {
        return supplier.get();
    }

    /**
     * Returns a {@code Supplier} which returns a single instance created by calling the specified {@code supplier.get()}.
     * 
     * @param supplier
     * @return
     */
    public static  Supplier single(final Supplier supplier) {
        return new Supplier() {
            private T instance = (T) NULL;

            @Override
            public T get() {
                synchronized (this) {
                    if (instance == NULL) {
                        instance = supplier.get();
                    }

                    return instance;
                }
            }
        };
    }

    public static com.landawn.abacus.util.function.Runnable close(final AutoCloseable closeable) {
        return new com.landawn.abacus.util.function.Runnable() {
            private volatile boolean isClosed = false;

            @Override
            public void run() {
                if (isClosed) {
                    return;
                }

                isClosed = true;
                IOUtil.close(closeable);
            }
        };
    }

    @SafeVarargs
    public static com.landawn.abacus.util.function.Runnable closeAll(final AutoCloseable... a) {
        return new com.landawn.abacus.util.function.Runnable() {
            private volatile boolean isClosed = false;

            @Override
            public void run() {
                if (isClosed) {
                    return;
                }

                isClosed = true;
                IOUtil.closeAll(a);
            }
        };
    }

    public static com.landawn.abacus.util.function.Runnable closeQuietly(final AutoCloseable closeable) {
        return new com.landawn.abacus.util.function.Runnable() {
            private volatile boolean isClosed = false;

            @Override
            public void run() {
                if (isClosed) {
                    return;
                }

                isClosed = true;
                IOUtil.closeQuietly(closeable);
            }
        };
    }

    @SafeVarargs
    public static com.landawn.abacus.util.function.Runnable closeAllQuietly(final AutoCloseable... a) {
        return new com.landawn.abacus.util.function.Runnable() {
            private volatile boolean isClosed = false;

            @Override
            public void run() {
                if (isClosed) {
                    return;
                }

                isClosed = true;
                IOUtil.closeAllQuietly(a);
            }
        };
    }

    public static com.landawn.abacus.util.function.Runnable emptyAction() {
        return EMPTY_ACTION;
    }

    public static  Consumer doNothing() {
        return DO_NOTHING;
    }

    public static  Consumer close() {
        return (Consumer) CLOSE;
    }

    public static  Consumer closeQuietly() {
        return (Consumer) CLOSE_QUIETLY;
    }

    public static  Consumer println() {
        return PRINTLN;
    }

    public static  BiConsumer println(final String separator) {
        N.checkArgNotNull(separator);

        switch (separator) {
            case "=":
                return PRINTLN_EQUAL;

            case ":":
                return PRINTLN_COLON;

            case ": ":
                return PRINTLN_COLON_SPACE;

            case "-":
                return PRINTLN_HYPHEN;

            case "_":
                return PRINTLN_UNDERSCORE;

            case ",":
                return PRINTLN_COMMA;

            case ", ":
                return PRINTLN_COMMA_SPACE;

            case "":
                return PRINTLN_EMPTY;

            default:
                return new BiConsumer() {
                    @Override
                    public void accept(T t, U u) {
                        N.println(t + separator + u);
                    }
                };
        }
    }

    public static  Function toStr() {
        return TO_STRING;
    }

    public static Function toCamelCase() {
        return TO_CAMEL_CASE;
    }

    public static Function toLowerCase() {
        return TO_LOWER_CASE;
    }

    public static Function toLowerCaseWithUnderscore() {
        return TO_LOWER_CASE_WITH_UNDERSCORE;
    }

    public static Function toUpperCase() {
        return TO_UPPER_CASE;
    }

    public static Function toUpperCaseWithUnderscore() {
        return TO_UPPER_CASE_WITH_UNDERSCORE;
    }

    public static  Function identity() {
        return IDENTITY;
    }

    public static  Function> keyed(final Function keyExtractor) {
        N.checkArgNotNull(keyExtractor);

        return new Function>() {
            @Override
            public Keyed apply(T t) {
                return Keyed.of(keyExtractor.apply(t), t);
            }
        };
    }

    private static final Function, Object>, Object> KK = new Function, Object>, Object>() {
        @Override
        public Object apply(Map.Entry, Object> t) {
            return t.getKey().val();
        }
    };

    @SuppressWarnings("rawtypes")
    public static  Function, Long>, T> kk() {
        return (Function) KK;
    }

    public static  Function> wrap() {
        return new Function>() {
            @Override
            public Wrapper apply(T t) {
                return Wrapper.of(t);
            }
        };
    }

    public static  Function> wrap(final ToIntFunction hashFunction, final BiPredicate equalsFunction) {
        N.checkArgNotNull(hashFunction);
        N.checkArgNotNull(equalsFunction);

        return new Function>() {
            @Override
            public Wrapper apply(T t) {
                return Wrapper.of(t, hashFunction, equalsFunction);
            }
        };
    }

    @SuppressWarnings("rawtypes")
    public static  Function, K> key() {
        return (Function) KEY;
    }

    @SuppressWarnings("rawtypes")
    public static  Function, V> value() {
        return (Function) VALUE;
    }

    @SuppressWarnings("rawtypes")
    public static  Function, Entry> inverse() {
        return (Function) INVERSE;
    }

    @SuppressWarnings("rawtypes")
    public static  BiFunction> entry() {
        // return (BiFunction) ENTRY;

        return (BiFunction) PAIR;
    }

    public static  Function> entry(final K key) {
        return new Function>() {
            @Override
            public Entry apply(T t) {
                return Pair.of(key, t);
            }
        };
    }

    public static  Function> entry(final Function keyExtractor) {
        N.checkArgNotNull(keyExtractor);

        return new Function>() {
            @Override
            public Entry apply(T t) {
                return Pair.of(keyExtractor.apply(t), t);
            }
        };
    }

    @SuppressWarnings("rawtypes")
    public static  BiFunction> pair() {
        return (BiFunction) PAIR;
    }

    @SuppressWarnings("rawtypes")
    public static  TriFunction> triple() {
        return (TriFunction) TRIPLE;
    }

    @SuppressWarnings("rawtypes")
    public static  Function> tuple1() {
        return (Function) TUPLE_1;
    }

    @SuppressWarnings("rawtypes")
    public static  BiFunction> tuple2() {
        return (BiFunction) TUPLE_2;
    }

    @SuppressWarnings("rawtypes")
    public static  TriFunction> tuple3() {
        return (TriFunction) TUPLE_3;
    }

    @SuppressWarnings({ "rawtypes" })
    public static  QuadFunction> tuple4() {
        return (QuadFunction) TUPLE_4;
    }

    public static Function trim() {
        return TRIM;
    }

    public static Function trimToEmpty() {
        return TRIM_TO_EMPTY;
    }

    public static Function trimToNull() {
        return TRIM_TO_NULL;
    }

    public static Function nullToEmpty() {
        return NULL_TO_EMPTY;
    }

    @SuppressWarnings("rawtypes")
    public static  Function, List> nullToEmptyL() {
        return (Function) NULL_TO_EMPTY_L;
    }

    @SuppressWarnings("rawtypes")
    public static  Function, Set> nullToEmptyS() {
        return (Function) NULL_TO_EMPTY_S;
    }

    @SuppressWarnings("rawtypes")
    public static  Function, Map> nullToEmptyM() {
        return (Function) NULL_TO_EMPTY_M;
    }

    public static Function length() {
        return LENGTH;
    }

    @SuppressWarnings("rawtypes")
    public static  Function size() {
        return (Function) SIZE;
    }

    public static  Function cast(final Class clazz) {
        N.checkArgNotNull(clazz);

        return new Function() {
            @Override
            public U apply(T t) {
                return (U) t;
            }
        };
    }

    public static  Predicate alwaysTrue() {
        return ALWAYS_TRUE;
    }

    public static  Predicate alwaysFalse() {
        return ALWAYS_FALSE;
    }

    public static  Predicate isNull() {
        return IS_NULL;
    }

    public static  Predicate isNullOrEmpty() {
        return (Predicate) IS_NULL_OR_EMPTY;
    }

    public static  Predicate isNullOrEmptyOrBlank() {
        return (Predicate) IS_NULL_OR_EMPTY_OR_BLANK;
    }

    public static  Predicate notNull() {
        return NOT_NULL;
    }

    public static  Predicate notNullOrEmpty() {
        return (Predicate) NOT_NULL_OR_EMPTY;
    }

    public static  Predicate notNullOrEmptyOrBlank() {
        return (Predicate) NOT_NULL_OR_EMPTY_OR_BLANK;
    }

    public static  Predicate equal(final Object target) {
        return new Predicate() {
            @Override
            public boolean test(T value) {
                return N.equals(value, target);
            }
        };
    }

    public static  Predicate notEqual(final Object target) {
        return new Predicate() {
            @Override
            public boolean test(T value) {
                return !N.equals(value, target);
            }
        };
    }

    @SuppressWarnings("rawtypes")
    public static  Predicate greaterThan(final T target) {
        return new Predicate() {
            @Override
            public boolean test(T value) {
                return N.compare(value, target) > 0;
            }
        };
    }

    @SuppressWarnings("rawtypes")
    public static  Predicate greaterEqual(final T target) {
        return new Predicate() {
            @Override
            public boolean test(T value) {
                return N.compare(value, target) >= 0;
            }
        };
    }

    @SuppressWarnings("rawtypes")
    public static  Predicate lessThan(final T target) {
        return new Predicate() {
            @Override
            public boolean test(T value) {
                return N.compare(value, target) < 0;
            }
        };
    }

    @SuppressWarnings("rawtypes")
    public static  Predicate lessEqual(final T target) {
        return new Predicate() {
            @Override
            public boolean test(T value) {
                return N.compare(value, target) <= 0;
            }
        };
    }

    /**
     * Checks if the value/element: {@code minValue < e < maxValue}.
     * 
     * @param minValue
     * @param maxValue
     * @return
     */
    @SuppressWarnings("rawtypes")
    public static  Predicate between(final T minValue, final T maxValue) {
        return new Predicate() {
            @Override
            public boolean test(T value) {
                return N.compare(value, minValue) > 0 && N.compare(value, maxValue) < 0;
            }
        };
    }

    public static  Predicate in(final Collection c) {
        N.checkArgNotNull(c);

        return new Predicate() {
            @Override
            public boolean test(T value) {
                return c.contains(value);
            }
        };
    }

    public static  Predicate notIn(final Collection c) {
        N.checkArgNotNull(c);

        return new Predicate() {
            @Override
            public boolean test(T value) {
                return !c.contains(value);
            }
        };
    }

    public static  Predicate instanceOf(final Class clazz) {
        N.checkArgNotNull(clazz);

        return new Predicate() {
            @Override
            public boolean test(T value) {
                return clazz.isInstance(value);
            }
        };
    }

    @SuppressWarnings("rawtypes")
    public static Predicate subtypeOf(final Class clazz) {
        N.checkArgNotNull(clazz);

        return new Predicate() {
            @Override
            public boolean test(Class value) {
                return clazz.isAssignableFrom(value);
            }
        };
    }

    public static Predicate startsWith(final String prefix) {
        N.checkArgNotNull(prefix);

        return new Predicate() {
            @Override
            public boolean test(String value) {
                return value.startsWith(prefix);
            }
        };
    }

    public static Predicate endsWith(final String suffix) {
        N.checkArgNotNull(suffix);

        return new Predicate() {
            @Override
            public boolean test(String value) {
                return value.endsWith(suffix);
            }
        };
    }

    public static Predicate contains(final String str) {
        N.checkArgNotNull(str);

        return new Predicate() {
            @Override
            public boolean test(String value) {
                return value.contains(str);
            }
        };
    }

    public static Predicate matches(final Pattern pattern) {
        N.checkArgNotNull(pattern);

        return new Predicate() {
            @Override
            public boolean test(CharSequence value) {
                return pattern.matcher(value).find();
            }
        };
    }

    public static  BiPredicate equal() {
        return BiPredicates.EQUAL;
    }

    public static  BiPredicate notEqual() {
        return BiPredicates.NOT_EQUAL;
    }

    @SuppressWarnings("rawtypes")
    public static  BiPredicate greaterThan() {
        return (BiPredicate) BiPredicates.GREATER_THAN;
    }

    @SuppressWarnings("rawtypes")
    public static  BiPredicate greaterEqual() {
        return (BiPredicate) BiPredicates.GREATER_EQUAL;
    }

    @SuppressWarnings("rawtypes")
    public static  BiPredicate lessThan() {
        return (BiPredicate) BiPredicates.LESS_THAN;
    }

    @SuppressWarnings("rawtypes")
    public static  BiPredicate lessEqual() {
        return (BiPredicate) BiPredicates.LESS_EQUAL;
    }

    public static  Predicate not(final Predicate predicate) {
        N.checkArgNotNull(predicate);

        return new Predicate() {
            @Override
            public boolean test(T t) {
                return !predicate.test(t);
            }
        };
    }

    public static  BiPredicate not(final BiPredicate biPredicate) {
        N.checkArgNotNull(biPredicate);

        return new BiPredicate() {
            @Override
            public boolean test(T t, U u) {
                return !biPredicate.test(t, u);
            }
        };
    }

    public static  TriPredicate not(final TriPredicate triPredicate) {
        N.checkArgNotNull(triPredicate);

        return new TriPredicate() {
            @Override
            public boolean test(A a, B b, C c) {
                return !triPredicate.test(a, b, c);
            }
        };
    }

    public static BooleanSupplier and(final BooleanSupplier first, final BooleanSupplier second) {
        N.checkArgNotNull(first);
        N.checkArgNotNull(second);

        return new BooleanSupplier() {
            @Override
            public boolean getAsBoolean() {
                return first.getAsBoolean() && second.getAsBoolean();
            }
        };
    }

    public static BooleanSupplier and(final BooleanSupplier first, final BooleanSupplier second, final BooleanSupplier third) {
        N.checkArgNotNull(first);
        N.checkArgNotNull(second);
        N.checkArgNotNull(third);

        return new BooleanSupplier() {
            @Override
            public boolean getAsBoolean() {
                return first.getAsBoolean() && second.getAsBoolean() && third.getAsBoolean();
            }
        };
    }

    public static  Predicate and(final Predicate first, final Predicate second) {
        N.checkArgNotNull(first);
        N.checkArgNotNull(second);

        return new Predicate() {
            @Override
            public boolean test(T t) {
                return first.test(t) && second.test(t);
            }
        };
    }

    public static  Predicate and(final Predicate first, final Predicate second, final Predicate third) {
        N.checkArgNotNull(first);
        N.checkArgNotNull(second);
        N.checkArgNotNull(third);

        return new Predicate() {
            @Override
            public boolean test(T t) {
                return first.test(t) && second.test(t) && third.test(t);
            }
        };
    }

    public static  Predicate and(final Collection> c) {
        N.checkArgNotNullOrEmpty(c, "c");

        return new Predicate() {
            @Override
            public boolean test(T t) {
                for (Predicate p : c) {
                    if (p.test(t) == false) {
                        return false;
                    }
                }

                return true;
            }
        };
    }

    public static  BiPredicate and(final BiPredicate first, final BiPredicate second) {
        N.checkArgNotNull(first);
        N.checkArgNotNull(second);

        return new BiPredicate() {
            @Override
            public boolean test(T t, U u) {
                return first.test(t, u) && second.test(t, u);
            }
        };
    }

    public static  BiPredicate and(final BiPredicate first, final BiPredicate second,
            final BiPredicate third) {
        N.checkArgNotNull(first);
        N.checkArgNotNull(second);
        N.checkArgNotNull(third);

        return new BiPredicate() {
            @Override
            public boolean test(T t, U u) {
                return first.test(t, u) && second.test(t, u) && third.test(t, u);
            }
        };
    }

    public static  BiPredicate and(final List> c) {
        N.checkArgNotNullOrEmpty(c, "c");

        return new BiPredicate() {
            @Override
            public boolean test(T t, U u) {
                for (BiPredicate p : c) {
                    if (p.test(t, u) == false) {
                        return false;
                    }
                }

                return true;
            }
        };
    }

    public static BooleanSupplier or(final BooleanSupplier first, final BooleanSupplier second) {
        N.checkArgNotNull(first);
        N.checkArgNotNull(second);

        return new BooleanSupplier() {
            @Override
            public boolean getAsBoolean() {
                return first.getAsBoolean() || second.getAsBoolean();
            }
        };
    }

    public static BooleanSupplier or(final BooleanSupplier first, final BooleanSupplier second, final BooleanSupplier third) {
        N.checkArgNotNull(first);
        N.checkArgNotNull(second);
        N.checkArgNotNull(third);

        return new BooleanSupplier() {
            @Override
            public boolean getAsBoolean() {
                return first.getAsBoolean() || second.getAsBoolean() || third.getAsBoolean();
            }
        };
    }

    public static  Predicate or(final Predicate first, final Predicate second) {
        N.checkArgNotNull(first);
        N.checkArgNotNull(second);

        return new Predicate() {
            @Override
            public boolean test(T t) {
                return first.test(t) || second.test(t);
            }
        };
    }

    public static  Predicate or(final Predicate first, final Predicate second, final Predicate third) {
        N.checkArgNotNull(first);
        N.checkArgNotNull(second);
        N.checkArgNotNull(third);

        return new Predicate() {
            @Override
            public boolean test(T t) {
                return first.test(t) || second.test(t) || third.test(t);
            }
        };
    }

    public static  Predicate or(final Collection> c) {
        N.checkArgNotNullOrEmpty(c, "c");

        return new Predicate() {
            @Override
            public boolean test(T t) {
                for (Predicate p : c) {
                    if (p.test(t)) {
                        return true;
                    }
                }

                return false;
            }
        };
    }

    public static  BiPredicate or(final BiPredicate first, final BiPredicate second) {
        N.checkArgNotNull(first);
        N.checkArgNotNull(second);

        return new BiPredicate() {
            @Override
            public boolean test(T t, U u) {
                return first.test(t, u) || second.test(t, u);
            }
        };
    }

    public static  BiPredicate or(final BiPredicate first, final BiPredicate second,
            final BiPredicate third) {
        N.checkArgNotNull(first);
        N.checkArgNotNull(second);
        N.checkArgNotNull(third);

        return new BiPredicate() {
            @Override
            public boolean test(T t, U u) {
                return first.test(t, u) || second.test(t, u) || third.test(t, u);
            }
        };
    }

    public static  BiPredicate or(final List> c) {
        N.checkArgNotNullOrEmpty(c, "c");

        return new BiPredicate() {
            @Override
            public boolean test(T t, U u) {
                for (BiPredicate p : c) {
                    if (p.test(t, u)) {
                        return true;
                    }
                }

                return false;
            }
        };
    }

    public static  Predicate> testByKey(final Predicate predicate) {
        N.checkArgNotNull(predicate);

        return new Predicate>() {
            @Override
            public boolean test(Entry entry) {
                return predicate.test(entry.getKey());
            }
        };
    }

    public static  Predicate> testByValue(final Predicate predicate) {
        N.checkArgNotNull(predicate);

        return new Predicate>() {
            @Override
            public boolean test(Entry entry) {
                return predicate.test(entry.getValue());
            }
        };
    }

    /**
     * Returns the specified instance.
     * 
     * @param predicate
     * @return
     * @deprecated replaced by {@link Fn#p(Predicate)}.
     */
    @Deprecated
    public static  Predicate test(final Predicate predicate) {
        return predicate;
    }

    /**
     * Returns the specified instance.
     * 
     * @param predicate
     * @return
     * @deprecated replaced by {@link Fn#p(BiPredicate)}.
     */
    @Deprecated
    public static  BiPredicate test(final BiPredicate predicate) {
        return predicate;
    }

    /**
     * Returns the specified instance.
     * 
     * @param predicate
     * @return
     * @deprecated
     */
    @Deprecated
    public static  TriPredicate test(final TriPredicate predicate) {
        return predicate;
    }

    public static  Consumer> acceptByKey(final Consumer consumer) {
        N.checkArgNotNull(consumer);

        return new Consumer>() {
            @Override
            public void accept(Entry entry) {
                consumer.accept(entry.getKey());
            }
        };
    }

    public static  Consumer> acceptByValue(final Consumer consumer) {
        N.checkArgNotNull(consumer);

        return new Consumer>() {
            @Override
            public void accept(Entry entry) {
                consumer.accept(entry.getValue());
            }
        };
    }

    public static  Function, R> applyByKey(final Function func) {
        N.checkArgNotNull(func);

        return new Function, R>() {
            @Override
            public R apply(Entry entry) {
                return func.apply(entry.getKey());
            }
        };
    }

    public static  Function, R> applyByValue(final Function func) {
        N.checkArgNotNull(func);

        return new Function, R>() {
            @Override
            public R apply(Entry entry) {
                return func.apply(entry.getValue());
            }
        };
    }

    public static  Function, Map.Entry> mapKey(final Function func) {
        N.checkArgNotNull(func);

        return new Function, Map.Entry>() {
            @Override
            public Map.Entry apply(Entry entry) {
                return Pair.of(func.apply(entry.getKey()), entry.getValue());
            }
        };
    }

    public static  Function, Map.Entry> mapValue(final Function func) {
        N.checkArgNotNull(func);

        return new Function, Map.Entry>() {
            @Override
            public Map.Entry apply(Entry entry) {
                return Pair.of(entry.getKey(), func.apply(entry.getValue()));
            }
        };
    }

    public static  Predicate> testKeyVal(final BiPredicate predicate) {
        N.checkArgNotNull(predicate);

        return new Predicate>() {
            @Override
            public boolean test(Entry entry) {
                return predicate.test(entry.getKey(), entry.getValue());
            }
        };
    }

    public static  Consumer> acceptKeyVal(final BiConsumer consumer) {
        N.checkArgNotNull(consumer);

        return new Consumer>() {
            @Override
            public void accept(Entry entry) {
                consumer.accept(entry.getKey(), entry.getValue());
            }
        };
    }

    public static  Function, R> applyKeyVal(final BiFunction func) {
        N.checkArgNotNull(func);

        return new Function, R>() {
            @Override
            public R apply(Entry entry) {
                return func.apply(entry.getKey(), entry.getValue());
            }
        };
    }

    public static ToByteFunction unboxB() {
        return ToByteFunction.UNBOX;
    }

    public static ToCharFunction unboxC() {
        return ToCharFunction.UNBOX;
    }

    public static ToShortFunction unboxS() {
        return ToShortFunction.UNBOX;
    }

    public static ToIntFunction unboxI() {
        return ToIntFunction.UNBOX;
    }

    public static ToLongFunction unboxL() {
        return ToLongFunction.UNBOX;
    }

    public static ToFloatFunction unboxF() {
        return ToFloatFunction.UNBOX;
    }

    public static ToDoubleFunction unboxD() {
        return ToDoubleFunction.UNBOX;
    }

    @SuppressWarnings({ "unchecked", "rawtypes" })
    public static  ToIntFunction numToInt() {
        return (ToIntFunction) NUM_TO_INT_FUNC;
    }

    @SuppressWarnings({ "unchecked", "rawtypes" })
    public static  ToLongFunction numToLong() {
        return (ToLongFunction) NUM_TO_LONG_FUNC;
    }

    @SuppressWarnings({ "unchecked", "rawtypes" })
    public static  ToDoubleFunction numToDouble() {
        return (ToDoubleFunction) NUM_TO_DOUBLE_FUNC;
    }

    /**
     * 
     * @param limit
     * @param predicate
     * @return
     */
    public static  Predicate limitThenFilter(final int limit, final Predicate predicate) {
        N.checkArgNotNull(predicate);

        return new Predicate() {
            private final AtomicInteger counter = new AtomicInteger(limit);

            @Override
            public boolean test(T t) {
                return counter.getAndDecrement() > 0 && predicate.test(t);
            }
        };
    }

    public static  BiPredicate limitThenFilter(final int limit, final BiPredicate predicate) {
        N.checkArgNotNull(predicate);

        return new BiPredicate() {
            private final AtomicInteger counter = new AtomicInteger(limit);

            @Override
            public boolean test(T t, U u) {
                return counter.getAndDecrement() > 0 && predicate.test(t, u);
            }
        };
    }

    public static  Predicate filterThenLimit(final Predicate predicate, final int limit) {
        N.checkArgNotNull(predicate);

        return new Predicate() {
            private final AtomicInteger counter = new AtomicInteger(limit);

            @Override
            public boolean test(T t) {
                return predicate.test(t) && counter.getAndDecrement() > 0;
            }
        };
    }

    public static  BiPredicate filterThenLimit(final BiPredicate predicate, final int limit) {
        N.checkArgNotNull(predicate);

        return new BiPredicate() {
            private final AtomicInteger counter = new AtomicInteger(limit);

            @Override
            public boolean test(T t, U u) {
                return predicate.test(t, u) && counter.getAndDecrement() > 0;
            }
        };
    }

    /**
     * Returns a stateful Function which should not be used in parallel stream.
     * 
     * @return
     */
    public static  Function> indexed() {
        return new Function>() {
            private final MutableLong idx = new MutableLong(0);

            @Override
            public Indexed apply(T t) {
                return Indexed.of(t, idx.getAndIncrement());
            }
        };
    }

    /**
     * Returns a stateful Predicate which should not be used in parallel stream.
     * 
     * @param predicate
     * @return
     */
    public static  Predicate indexed(final IndexedPredicate predicate) {
        return Predicates.indexed(predicate);
    }

    /**
     * Returns a stateful BiPredicate which should not be used in parallel stream.
     * 
     * @param predicate
     * @return
     * @deprecated replaced by {@code BiPredicates#indexed(IndexedBiPredicate)}.
     */
    @Deprecated
    public static  BiPredicate indexed(final IndexedBiPredicate predicate) {
        return BiPredicates.indexed(predicate);
    }

    /**
     * Returns a stateful Function which should not be used in parallel stream.
     * 
     * @param func
     * @return
     * @deprecated replaced by {@code Functions#indexed(IndexedFunction)}.
     */
    @Deprecated
    public static  Function indexedd(final IndexedFunction func) {
        return Functions.indexed(func);
    }

    /**
     * Returns a stateful BiFunction which should not be used in parallel stream.
     * 
     * @param func
     * @return
     * @deprecated replaced by {@code BiFunctions#indexed(IndexedBiFunction)}.
     */
    @Deprecated
    public static  BiFunction indexedd(final IndexedBiFunction func) {
        return BiFunctions.indexed(func);
    }

    /**
     * Returns a stateful Consumer which should not be used in parallel stream.
     * 
     * @param action
     * @return
     * @deprecated replaced by {@code Consumers#indexed(IndexedConsumer)}.
     */
    @Deprecated
    public static  Consumer indexeed(final IndexedConsumer action) {
        return Consumers.indexed(action);
    }

    /**
     * Returns a stateful BiConsumer which should not be used in parallel stream.
     * 
     * @param action
     * @return
     * @deprecated replaced by {@code BiConsumers#indexed(IndexedBiConsumer)}.
     */
    @Deprecated
    public static  BiConsumer indexeed(final IndexedBiConsumer action) {
        return BiConsumers.indexed(action);
    }

    @SuppressWarnings("rawtypes")
    public static  Function compareTo(final T target) {
        return new Function() {
            @Override
            public Integer apply(T t) {
                return N.compare(t, target);
            }
        };
    }

    @SuppressWarnings("rawtypes")
    public static  Function compareTo(final T target, final Comparator cmp) {
        // N.checkArgNotNull(cmp);

        if (cmp == null || cmp == Comparators.naturalOrder()) {
            return (Function) compareTo((Comparable) target);
        }

        return new Function() {
            @Override
            public Integer apply(T t) {
                return N.compare(t, target, cmp);
            }
        };
    }

    @SuppressWarnings("rawtypes")
    public static  BiFunction compare() {
        return COMPARE;
    }

    public static  BiFunction compare(final Comparator cmp) {
        // N.checkArgNotNull(cmp);

        if (cmp == null || cmp == Comparators.naturalOrder()) {
            return COMPARE;
        }

        return new BiFunction() {
            @Override
            public Integer apply(T a, T b) {
                return N.compare(a, b, cmp);
            }
        };
    }

    @Beta
    public static  Predicate p(final Predicate predicate) {
        return predicate;
    }

    @Beta
    public static  Predicate p(final U u, final BiPredicate biPredicate) {
        return Predicates.create(u, biPredicate);
    }

    @Beta
    public static  Predicate p(final A a, final B b, final TriPredicate triPredicate) {
        N.checkArgNotNull(triPredicate);

        return new Predicate() {
            @Override
            public boolean test(T t) {
                return triPredicate.test(t, a, b);
            }
        };
    }

    @Beta
    public static  BiPredicate p(final BiPredicate biPredicate) {
        return biPredicate;
    }

    @Beta
    public static  Consumer c(final Consumer consumer) {
        return consumer;
    }

    @Beta
    public static  Consumer c(final U u, final BiConsumer biConsumer) {
        return Consumers.create(u, biConsumer);
    }

    @Beta
    public static  BiConsumer c(final BiConsumer biConsumer) {
        return biConsumer;
    }

    @Beta
    public static  Function f(final Function function) {
        return function;
    }

    @Beta
    public static  Function f(final U u, final BiFunction biFunction) {
        return Functions.create(u, biFunction);
    }

    @Beta
    public static  BiFunction f(final BiFunction biFunction) {
        return biFunction;
    }

    @Beta
    public static  Predicate pp(final Try.Predicate predicate) {
        N.checkArgNotNull(predicate);

        return new Predicate() {
            @Override
            public boolean test(T value) {
                try {
                    return predicate.test(value);
                } catch (Exception e) {
                    throw N.toRuntimeException(e);
                }
            }
        };
    }

    @Beta
    public static  Predicate pp(final U u, final Try.BiPredicate biPredicate) {
        N.checkArgNotNull(biPredicate);

        return new Predicate() {
            @Override
            public boolean test(T t) {
                try {
                    return biPredicate.test(t, u);
                } catch (Exception e) {
                    throw N.toRuntimeException(e);
                }
            }
        };
    }

    @Beta
    public static  Predicate pp(final A a, final B b, final Try.TriPredicate triPredicate) {
        N.checkArgNotNull(triPredicate);

        return new Predicate() {
            @Override
            public boolean test(T t) {
                try {
                    return triPredicate.test(t, a, b);
                } catch (Exception e) {
                    throw N.toRuntimeException(e);
                }
            }
        };
    }

    @Beta
    public static  BiPredicate pp(final Try.BiPredicate biPredicate) {
        N.checkArgNotNull(biPredicate);

        return new BiPredicate() {
            @Override
            public boolean test(T t, U u) {
                try {
                    return biPredicate.test(t, u);
                } catch (Exception e) {
                    throw N.toRuntimeException(e);
                }
            }
        };
    }

    @Beta
    public static  Consumer cc(final Try.Consumer consumer) {
        N.checkArgNotNull(consumer);

        return new Consumer() {
            @Override
            public void accept(T value) {
                try {
                    consumer.accept(value);
                } catch (Exception e) {
                    throw N.toRuntimeException(e);
                }
            }
        };
    }

    @Beta
    public static  Consumer cc(final U u, final Try.BiConsumer biConsumer) {
        N.checkArgNotNull(biConsumer);

        return new Consumer() {
            @Override
            public void accept(T t) {
                try {
                    biConsumer.accept(t, u);
                } catch (Exception e) {
                    throw N.toRuntimeException(e);
                }
            }
        };
    }

    @Beta
    public static  BiConsumer cc(final Try.BiConsumer biConsumer) {
        N.checkArgNotNull(biConsumer);

        return new BiConsumer() {
            @Override
            public void accept(T t, U u) {
                try {
                    biConsumer.accept(t, u);
                } catch (Exception e) {
                    throw N.toRuntimeException(e);
                }
            }
        };
    }

    @Beta
    public static  Function ff(final Try.Function function) {
        N.checkArgNotNull(function);

        return new Function() {
            @Override
            public R apply(T t) {
                try {
                    return function.apply(t);
                } catch (Exception e) {
                    throw N.toRuntimeException(e);
                }
            }
        };
    }

    @Beta
    public static  Function ff(final U u, final Try.BiFunction biFunction) {
        N.checkArgNotNull(biFunction);

        return new Function() {
            @Override
            public R apply(T t) {
                try {
                    return biFunction.apply(t, u);
                } catch (Exception e) {
                    throw N.toRuntimeException(e);
                }
            }
        };
    }

    @Beta
    public static  BiFunction ff(final Try.BiFunction biFunction) {
        N.checkArgNotNull(biFunction);

        return new BiFunction() {
            @Override
            public R apply(T t, U u) {
                try {
                    return biFunction.apply(t, u);
                } catch (Exception e) {
                    throw N.toRuntimeException(e);
                }
            }
        };
    }

    @Beta
    public static  Try.Predicate ep(final Try.Predicate predicate) {
        return predicate;
    }

    @Beta
    public static  Try.Predicate ep(final U u, final Try.BiPredicate biPredicate) {
        N.checkArgNotNull(biPredicate);

        return new Try.Predicate() {
            @Override
            public boolean test(T t) throws E {
                return biPredicate.test(t, u);
            }
        };
    }

    @Beta
    public static  Try.Predicate ep(final A a, final B b, final Try.TriPredicate triPredicate) {
        N.checkArgNotNull(triPredicate);

        return new Try.Predicate() {
            @Override
            public boolean test(T t) throws E {
                return triPredicate.test(t, a, b);
            }
        };
    }

    @Beta
    public static  Try.BiPredicate ep(final Try.BiPredicate biPredicate) {
        return biPredicate;
    }

    @Beta
    public static  Try.Consumer ec(final Try.Consumer consumer) {
        return consumer;
    }

    @Beta
    public static  Try.Consumer ec(final U u, final Try.BiConsumer biConsumer) {
        N.checkArgNotNull(biConsumer);

        return new Try.Consumer() {
            @Override
            public void accept(T t) throws E {
                biConsumer.accept(t, u);
            }
        };
    }

    @Beta
    public static  Try.BiConsumer ec(final Try.BiConsumer biConsumer) {
        return biConsumer;
    }

    @Beta
    public static  Try.Function ef(final Try.Function function) {
        return function;
    }

    @Beta
    public static  Try.Function ef(final U u, final Try.BiFunction biFunction) {
        N.checkArgNotNull(biFunction);

        return new Try.Function() {
            @Override
            public R apply(T t) throws E {
                return biFunction.apply(t, u);
            }
        };
    }

    @Beta
    public static  Try.BiFunction ef(final Try.BiFunction biFunction) {
        return biFunction;
    }

    /**
     * Synchronized {@code Predicate}
     * 
     * @param target to synchronized on
     * @param predicate 
     * @return
     */
    @Beta
    public static  Predicate sp(final Object target, final Predicate predicate) {
        N.checkArgNotNull(target, "target");
        N.checkArgNotNull(predicate, "predicate");

        return new Predicate() {
            @Override
            public boolean test(T t) {
                synchronized (target) {
                    return predicate.test(t);
                }
            }
        };
    }

    /**
     * Synchronized {@code Predicate}
     * 
     * @param target to synchronized on
     * @param u
     * @param biPredicate
     * @return
     */
    @Beta
    public static  Predicate sp(final Object target, final U u, final BiPredicate biPredicate) {
        N.checkArgNotNull(target, "target");
        N.checkArgNotNull(biPredicate, "biPredicate");

        return new Predicate() {
            @Override
            public boolean test(T t) {
                synchronized (target) {
                    return biPredicate.test(t, u);
                }
            }
        };
    }

    /**
     * Synchronized {@code Predicate}
     * 
     * @param target to synchronized on
     * @param a
     * @param b
     * @param triPredicate
     * @return
     */
    @Beta
    public static  Predicate sp(final Object target, final A a, final B b, final TriPredicate triPredicate) {
        N.checkArgNotNull(target, "target");
        N.checkArgNotNull(triPredicate, "triPredicate");

        return new Predicate() {
            @Override
            public boolean test(T t) {
                synchronized (target) {
                    return triPredicate.test(t, a, b);
                }
            }
        };
    }

    /**
     * Synchronized {@code BiPredicate}
     * 
     * @param target to synchronized on
     * @param biPredicate
     * @return
     */
    @Beta
    public static  BiPredicate sp(final Object target, final BiPredicate biPredicate) {
        N.checkArgNotNull(target, "target");
        N.checkArgNotNull(biPredicate, "biPredicate");

        return new BiPredicate() {
            @Override
            public boolean test(T t, U u) {
                synchronized (target) {
                    return biPredicate.test(t, u);
                }
            }
        };
    }

    /**
     * Synchronized {@code Consumer}
     * 
     * @param target to synchronized on
     * @param consumer
     * @return
     */
    @Beta
    public static  Consumer sc(final Object target, final Consumer consumer) {
        N.checkArgNotNull(target, "target");
        N.checkArgNotNull(consumer, "consumer");

        return new Consumer() {
            @Override
            public void accept(T t) {
                synchronized (target) {
                    consumer.accept(t);
                }
            }
        };
    }

    /**
     * Synchronized {@code Consumer}
     * 
     * @param target to synchronized on
     * @param u
     * @param biConsumer
     * @return
     */
    @Beta
    public static  Consumer sc(final Object target, final U u, final BiConsumer biConsumer) {
        N.checkArgNotNull(target, "target");
        N.checkArgNotNull(biConsumer, "biConsumer");

        return new Consumer() {
            @Override
            public void accept(T t) {
                synchronized (target) {
                    biConsumer.accept(t, u);
                }
            }
        };
    }

    /**
     * Synchronized {@code BiConsumer}
     * 
     * @param target to synchronized on
     * @param biConsumer
     * @return
     */
    @Beta
    public static  BiConsumer sc(final Object target, final BiConsumer biConsumer) {
        N.checkArgNotNull(target, "target");
        N.checkArgNotNull(biConsumer, "biConsumer");

        return new BiConsumer() {
            @Override
            public void accept(T t, U u) {
                synchronized (target) {
                    biConsumer.accept(t, u);
                }
            }
        };
    }

    /**
     * Synchronized {@code Function}
     * 
     * @param target to synchronized on
     * @param function
     * @return
     */
    @Beta
    public static  Function sf(final Object target, final Function function) {
        N.checkArgNotNull(target, "target");
        N.checkArgNotNull(function, "function");

        return new Function() {
            @Override
            public R apply(T t) {
                synchronized (target) {
                    return function.apply(t);
                }
            }
        };
    }

    /**
     * Synchronized {@code Function}
     * 
     * @param target to synchronized on
     * @param u
     * @param biFunction
     * @return
     */
    @Beta
    public static  Function sf(final Object target, final U u, final BiFunction biFunction) {
        N.checkArgNotNull(target, "target");
        N.checkArgNotNull(biFunction, "biFunction");

        return new Function() {
            @Override
            public R apply(T t) {
                synchronized (target) {
                    return biFunction.apply(t, u);
                }
            }
        };
    }

    /**
     * Synchronized {@code BiFunction}
     * 
     * @param target to synchronized on
     * @param biFunction
     * @return
     */
    @Beta
    public static  BiFunction sf(final Object target, final BiFunction biFunction) {
        N.checkArgNotNull(target, "target");
        N.checkArgNotNull(biFunction, "biFunction");

        return new BiFunction() {
            @Override
            public R apply(T t, U u) {
                synchronized (target) {
                    return biFunction.apply(t, u);
                }
            }
        };
    }

    public static  BinaryOperator throwingMerger() {
        return BinaryOperators.THROWING_MERGER;
    }

    public static  BinaryOperator ignoringMerger() {
        return BinaryOperators.IGNORING_MERGER;
    }

    public static  BinaryOperator replacingMerger() {
        return BinaryOperators.REPLACING_MERGER;
    }

    /**
     * 
     * @return
     * @deprecated replaced by {@code BiConsumers#ofAddAll()}
     */
    @Deprecated
    public static > BiConsumer addAll() {
        return BiConsumers. ofAddAll();
    }

    /**
     * 
     * @return
     * @deprecated replaced by {@code BiConsumers#ofPutAll()}
     */
    @Deprecated
    public static > BiConsumer putAll() {
        return BiConsumers. ofPutAll();
    }

    /**
     * 
     * @return
     * @see Collectors#toList()
     */
    public static  Collector> toList() {
        return Collectors.toList();
    }

    /**
     * 
     * @return
     * @see Collectors#toImmutableList()
     */
    public static  Collector> toImmutableList() {
        return Collectors.toImmutableList();
    }

    /**
     * 
     * @return
     * @see Collectors#toSet()
     */
    public static  Collector> toSet() {
        return Collectors.toSet();
    }

    /**
     * 
     * @return
     * @see Collectors#toImmutableSet()
     */
    public static  Collector> toImmutableSet() {
        return Collectors.toImmutableSet();
    }

    public static > Collector toCollection(Supplier collectionFactory) {
        return Collectors.toCollection(collectionFactory);
    }

    /**
     * 
     * @return
     * @see Collectors#toMap()
     */
    public static  Collector, ?, Map> toMap() {
        return Collectors.toMap();
    }

    /**
     * 
     * @param mergeFunction
     * @return
     * @see Collectors#toMap(BinaryOperator)
     */
    public static  Collector, ?, Map> toMap(final BinaryOperator mergeFunction) {
        return Collectors.toMap(mergeFunction);
    }

    /**
     * 
     * @param mapFactory
     * @return
     * @see Collectors#toMap(Supplier)
     */
    public static > Collector, ?, M> toMap(final Supplier mapFactory) {
        return Collectors.toMap(mapFactory);
    }

    /**
     * 
     * @param mergeFunction
     * @param mapFactory
     * @return
     * @see Collectors#toMap(BinaryOperator, Supplier)
     */
    public static > Collector, ?, M> toMap(final BinaryOperator mergeFunction, final Supplier mapFactory) {
        return Collectors.toMap(mergeFunction, mapFactory);
    }

    /**
     * 
     * @param keyExtractor
     * @param valueMapper
     * @return
     * @see Collectors#toMap(Function, Function)
     */
    public static  Collector> toMap(Function keyExtractor, Function valueMapper) {
        return Collectors.toMap(keyExtractor, valueMapper);
    }

    /**
     * 
     * @param keyExtractor
     * @param valueMapper
     * @param mergeFunction
     * @return
     * @see Collectors#toMap(Function, Function, BinaryOperator)
     */
    public static  Collector> toMap(Function keyExtractor, Function valueMapper,
            BinaryOperator mergeFunction) {
        return Collectors.toMap(keyExtractor, valueMapper, mergeFunction);
    }

    /**
     * 
     * @param keyExtractor
     * @param valueMapper
     * @param mapFactory
     * @return
     * @see Collectors#toMap(Function, Function, Supplier)
     */
    public static > Collector toMap(final Function keyExtractor,
            final Function valueMapper, final Supplier mapFactory) {
        return Collectors.toMap(keyExtractor, valueMapper, mapFactory);
    }

    /**
     * 
     * @param keyExtractor
     * @param valueMapper
     * @param mergeFunction
     * @param mapFactory
     * @return
     * @see Collectors#toMap(Function, Function, BinaryOperator, Supplier)
     */
    public static > Collector toMap(final Function keyExtractor,
            final Function valueMapper, final BinaryOperator mergeFunction, final Supplier mapFactory) {
        return Collectors.toMap(keyExtractor, valueMapper, mergeFunction, mapFactory);
    }

    /**
     * 
     * @param classifier
     * @param downstream
     * @return
     * @see Collectors#groupingBy(Function, Collector)
     */
    public static  Collector> toMap(final Function classifier,
            final Collector downstream) {
        return Collectors.toMap(classifier, downstream);
    }

    /**
     * 
     * @param classifier
     * @param downstream
     * @param mapFactory
     * @return
     * @see Collectors#groupingBy(Function, Collector, Supplier)
     */
    public static > Collector toMap(final Function classifier,
            final Collector downstream, final Supplier mapFactory) {
        return Collectors.toMap(classifier, downstream, mapFactory);
    }

    /**
     * 
     * @param classifier
     * @param valueMapper
     * @param downstream
     * @return
     * @see Collectors#groupingBy(Function, Collector)
     */
    public static  Collector> toMap(final Function classifier,
            final Function valueMapper, final Collector downstream) {
        return Collectors.toMap(classifier, valueMapper, downstream);
    }

    /**
     * 
     * @param classifier
     * @param valueMapper
     * @param downstream
     * @param mapFactory
     * @return
     * @see Collectors#groupingBy(Function, Collector, Supplier)
     */
    public static > Collector toMap(final Function classifier,
            final Function valueMapper, final Collector downstream, final Supplier mapFactory) {
        return Collectors.toMap(classifier, valueMapper, downstream, mapFactory);
    }

    /**
     * 
     * @return
     * @see Collectors#toImmutableMap()
     */
    public static  Collector, ?, ImmutableMap> toImmutableMap() {
        return Collectors.toImmutableMap(Fn.IDENTITY, Fn.IDENTITY);
    }

    /**
     * 
     * @param mergeFunction
     * @return
     * @see Collectors#toImmutableMap(BinaryOperator)
     */
    public static  Collector, ?, ImmutableMap> toImmutableMap(final BinaryOperator mergeFunction) {
        return Collectors.toImmutableMap(Fn.IDENTITY, Fn.IDENTITY, mergeFunction);
    }

    /**
     * 
     * @param keyExtractor
     * @param valueMapper
     * @return
     * @see Collectors#toImmutableMap(Function, Function)
     */
    public static  Collector> toImmutableMap(Function keyExtractor,
            Function valueMapper) {
        return Collectors.toImmutableMap(keyExtractor, valueMapper);
    }

    /**
     * 
     * @param keyExtractor
     * @param valueMapper
     * @param mergeFunction
     * @return
     * @see Collectors#toImmutableMap(Function, Function, BinaryOperator)
     */
    public static  Collector> toImmutableMap(Function keyExtractor,
            Function valueMapper, BinaryOperator mergeFunction) {
        return Collectors.toImmutableMap(keyExtractor, valueMapper, mergeFunction);
    }

    /**
     * 
     * @param classifier
     * @return
     * @see Collectors#groupingBy(Function)
     */
    public static  Collector>> groupingBy(Function classifier) {
        return Collectors.groupingBy(classifier);
    }

    /**
     * 
     * @param classifier
     * @param mapFactory
     * @return
     * @see Collectors#groupingBy(Function, Supplier)
     */
    public static >> Collector groupingBy(final Function classifier,
            final Supplier mapFactory) {
        return Collectors.groupingBy(classifier, mapFactory);
    }

    /**
     * 
     * @param classifier
     * @param downstream
     * @return
     * @see Collectors#groupingBy(Function, Collector)
     */
    public static  Collector> groupingBy(final Function classifier,
            final Collector downstream) {
        return Collectors.groupingBy(classifier, downstream);
    }

    /**
     * 
     * @param classifier
     * @param downstream
     * @param mapFactory
     * @return
     * @see Collectors#groupingBy(Function, Collector, Supplier)
     */
    public static > Collector groupingBy(final Function classifier,
            final Collector downstream, final Supplier mapFactory) {
        return Collectors.groupingBy(classifier, downstream, mapFactory);
    }

    /**
     * 
     * @param classifier
     * @return
     * @see Collectors#groupingBy(Function)
     */
    public static  Collector> countingBy(Function classifier) {
        return groupingBy(classifier, Collectors.counting());
    }

    /**
     * 
     * @param classifier
     * @param mapFactory
     * @return
     * @see Collectors#groupingBy(Function, Supplier)
     */
    public static > Collector countingBy(final Function classifier,
            final Supplier mapFactory) {
        return groupingBy(classifier, Collectors.counting(), mapFactory);
    }

    /**
     * 
     * @param classifier
     * @return
     * @see Collectors#groupingBy(Function)
     */
    public static  Collector> countingIntBy(Function classifier) {
        return groupingBy(classifier, Collectors.countingInt());
    }

    /**
     * 
     * @param classifier
     * @param mapFactory
     * @return
     * @see Collectors#groupingBy(Function, Supplier)
     */
    public static > Collector countingIntBy(final Function classifier,
            final Supplier mapFactory) {
        return groupingBy(classifier, Collectors.countingInt(), mapFactory);
    }

    /**
     * 
     * @return
     * @see Collectors#counting()
     */
    public static  Collector counting() {
        return Collectors.counting();
    }

    /**
     * 
     * @return
     * @see Collectors#countingInt()
     */
    public static  Collector countingInt() {
        return Collectors.countingInt();
    }

    /**
     * 
     * @param mapper
     * @return
     * @see Collectors#summingInt(ToIntFunction)
     */
    public static  Collector summingInt(final ToIntFunction mapper) {
        return Collectors.summingInt(mapper);
    }

    /**
     * 
     * @param mapper
     * @return
     * @see Collectors#summingLong(ToLongFunction)
     */
    public static  Collector summingLong(final ToLongFunction mapper) {
        return Collectors.summingLong(mapper);
    }

    /**
     * 
     * @param mapper
     * @return
     * @see Collectors#summarizingDouble(ToDoubleFunction)
     */
    public static  Collector summingDouble(final ToDoubleFunction mapper) {
        return Collectors.summingDouble(mapper);
    }

    /**
     * 
     * @param mapper
     * @return
     * @see Collectors#averagingInt(ToIntFunction)
     */
    public static  Collector averagingInt(final ToIntFunction mapper) {
        return Collectors.averagingInt(mapper);
    }

    /**
     * 
     * @param mapper
     * @return
     * @see Collectors#averagingLong(ToLongFunction)
     */
    public static  Collector averagingLong(final ToLongFunction mapper) {
        return Collectors.averagingLong(mapper);
    }

    /**
     * 
     * @param mapper
     * @return
     * @see Collectors#averagingDouble(ToDoubleFunction)
     */
    public static  Collector averagingDouble(final ToDoubleFunction mapper) {
        return Collectors.averagingDouble(mapper);
    }

    public static  Collector> filtering(final Predicate predicate) {
        return Collectors.filtering(predicate);
    }

    public static  Collector filtering(final Predicate predicate, final Collector downstream) {
        return Collectors.filtering(predicate, downstream);
    }

    public static  Collector> mapping(final Function mapper) {
        return Collectors.mapping(mapper);
    }

    public static  Collector mapping(final Function mapper, final Collector downstream) {
        return Collectors.mapping(mapper, downstream);
    }

    public static  Collector> flatMapping(final Function> mapper) {
        return Collectors.flatMapping(mapper);
    }

    public static  Collector flatMapping(final Function> mapper,
            final Collector downstream) {
        return Collectors.flatMapping(mapper, downstream);
    }

    public static  Collector> flattMapping(final Function> mapper) {
        return Collectors.flattMapping(mapper);
    }

    public static  Collector flattMapping(final Function> mapper,
            final Collector downstream) {
        return Collectors.flattMapping(mapper, downstream);
    }

    public static  Collector, Tuple2> combine(final Collector collector1,
            final Collector collector2) {
        return Collectors.combine(collector1, collector2);
    }

    public static  Collector, Tuple3> combine(final Collector collector1,
            final Collector collector2, final Collector collector3) {
        return Collectors.combine(collector1, collector2, collector3);
    }

    public static class Factory {
        private static final IntFunction BOOLEAN_ARRAY = new IntFunction() {
            @Override
            public boolean[] apply(int len) {
                return new boolean[len];
            }
        };

        private static final IntFunction CHAR_ARRAY = new IntFunction() {
            @Override
            public char[] apply(int len) {
                return new char[len];
            }
        };

        private static final IntFunction BYTE_ARRAY = new IntFunction() {
            @Override
            public byte[] apply(int len) {
                return new byte[len];
            }
        };

        private static final IntFunction SHORT_ARRAY = new IntFunction() {
            @Override
            public short[] apply(int len) {
                return new short[len];
            }
        };

        private static final IntFunction INT_ARRAY = new IntFunction() {
            @Override
            public int[] apply(int len) {
                return new int[len];
            }
        };

        private static final IntFunction LONG_ARRAY = new IntFunction() {
            @Override
            public long[] apply(int len) {
                return new long[len];
            }
        };

        private static final IntFunction FLOAT_ARRAY = new IntFunction() {
            @Override
            public float[] apply(int len) {
                return new float[len];
            }
        };

        private static final IntFunction DOUBLE_ARRAY = new IntFunction() {
            @Override
            public double[] apply(int len) {
                return new double[len];
            }
        };

        private static final IntFunction STRING_ARRAY = new IntFunction() {
            @Override
            public String[] apply(int len) {
                return new String[len];
            }
        };

        private static final IntFunction OBJECT_ARRAY = new IntFunction() {
            @Override
            public Object[] apply(int len) {
                return new Object[len];
            }
        };

        private static final IntFunction BOOLEAN_LIST = new IntFunction() {
            @Override
            public BooleanList apply(int len) {
                return new BooleanList(len);
            }
        };

        private static final IntFunction CHAR_LIST = new IntFunction() {
            @Override
            public CharList apply(int len) {
                return new CharList(len);
            }
        };

        private static final IntFunction BYTE_LIST = new IntFunction() {
            @Override
            public ByteList apply(int len) {
                return new ByteList(len);
            }
        };

        private static final IntFunction SHORT_LIST = new IntFunction() {
            @Override
            public ShortList apply(int len) {
                return new ShortList(len);
            }
        };

        private static final IntFunction INT_LIST = new IntFunction() {
            @Override
            public IntList apply(int len) {
                return new IntList(len);
            }
        };

        private static final IntFunction LONG_LIST = new IntFunction() {
            @Override
            public LongList apply(int len) {
                return new LongList(len);
            }
        };

        private static final IntFunction FLOAT_LIST = new IntFunction() {
            @Override
            public FloatList apply(int len) {
                return new FloatList(len);
            }
        };

        private static final IntFunction DOUBLE_LIST = new IntFunction() {
            @Override
            public DoubleList apply(int len) {
                return new DoubleList(len);
            }
        };
        @SuppressWarnings("rawtypes")
        private static final IntFunction LIST_FACTORY = new IntFunction() {
            @Override
            public List apply(int len) {
                return new ArrayList<>(len);
            }
        };

        @SuppressWarnings("rawtypes")
        private static final IntFunction LINKED_LIST_FACTORY = new IntFunction() {
            @Override
            public LinkedList apply(int len) {
                return new LinkedList<>();
            }
        };

        @SuppressWarnings("rawtypes")
        private static final IntFunction SET_FACTORY = new IntFunction() {
            @Override
            public Set apply(int len) {
                return new HashSet<>(N.initHashCapacity(len));
            }
        };

        @SuppressWarnings("rawtypes")
        private static final IntFunction LINKED_HASH_SET_FACTORY = new IntFunction() {
            @Override
            public LinkedHashSet apply(int len) {
                return new LinkedHashSet<>(N.initHashCapacity(len));
            }
        };

        @SuppressWarnings("rawtypes")
        private static final IntFunction TREE_SET_FACTORY = new IntFunction() {
            @Override
            public TreeSet apply(int len) {
                return new TreeSet<>();
            }
        };

        @SuppressWarnings("rawtypes")
        private static final IntFunction QUEUE_FACTORY = new IntFunction() {
            @Override
            public Queue apply(int len) {
                return new LinkedList();
            }
        };

        @SuppressWarnings("rawtypes")
        private static final IntFunction DEQUE_FACTORY = new IntFunction() {
            @Override
            public Deque apply(int len) {
                return new LinkedList();
            }
        };

        @SuppressWarnings("rawtypes")
        private static final IntFunction ARRAY_DEQUE_FACTORY = new IntFunction() {
            @Override
            public ArrayDeque apply(int len) {
                return new ArrayDeque(len);
            }
        };

        @SuppressWarnings("rawtypes")
        private static final IntFunction LINKED_BLOCKING_QUEUE_FACTORY = new IntFunction() {
            @Override
            public LinkedBlockingQueue apply(int len) {
                return new LinkedBlockingQueue(len);
            }
        };

        @SuppressWarnings("rawtypes")
        private static final IntFunction CONCURRENT_LINKED_QUEUE_FACTORY = new IntFunction() {
            @Override
            public ConcurrentLinkedQueue apply(int len) {
                return new ConcurrentLinkedQueue();
            }
        };

        @SuppressWarnings("rawtypes")
        private static final IntFunction PRIORITY_QUEUE_FACTORY = new IntFunction() {
            @Override
            public PriorityQueue apply(int len) {
                return new PriorityQueue(len);
            }
        };

        @SuppressWarnings("rawtypes")
        private static final IntFunction MAP_FACTORY = new IntFunction() {
            @Override
            public Map apply(int len) {
                return new HashMap<>(N.initHashCapacity(len));
            }
        };

        @SuppressWarnings("rawtypes")
        private static final IntFunction LINKED_HASH_MAP_FACTORY = new IntFunction() {
            @Override
            public LinkedHashMap apply(int len) {
                return new LinkedHashMap<>(N.initHashCapacity(len));
            }
        };

        @SuppressWarnings("rawtypes")
        private static final IntFunction IDENTITY_HASH_MAP_FACTORY = new IntFunction() {
            @Override
            public IdentityHashMap apply(int len) {
                return new IdentityHashMap<>(N.initHashCapacity(len));
            }
        };

        @SuppressWarnings("rawtypes")
        private static final IntFunction TREE_MAP_FACTORY = new IntFunction() {
            @Override
            public TreeMap apply(int len) {
                return new TreeMap<>();
            }
        };

        @SuppressWarnings("rawtypes")
        private static final IntFunction CONCURRENT_HASH_MAP_FACTORY = new IntFunction() {
            @Override
            public ConcurrentHashMap apply(int len) {
                return new ConcurrentHashMap(N.initHashCapacity(len));
            }
        };

        @SuppressWarnings("rawtypes")
        private static final IntFunction BI_MAP_FACTORY = new IntFunction() {
            @Override
            public BiMap apply(int len) {
                return new BiMap(N.initHashCapacity(len));
            }
        };

        @SuppressWarnings("rawtypes")
        private static final IntFunction MULTISET_FACTORY = new IntFunction() {
            @Override
            public Multiset apply(int len) {
                return new Multiset(N.initHashCapacity(len));
            }
        };

        @SuppressWarnings("rawtypes")
        private static final IntFunction LONG_MULTISET_FACTORY = new IntFunction() {
            @Override
            public LongMultiset apply(int len) {
                return new LongMultiset(N.initHashCapacity(len));
            }
        };

        @SuppressWarnings("rawtypes")
        private static final IntFunction LIST_MULTIMAP_FACTORY = new IntFunction() {
            @Override
            public ListMultimap apply(int len) {
                return new ListMultimap(N.initHashCapacity(len));
            }
        };

        @SuppressWarnings("rawtypes")
        private static final IntFunction SET_MULTIMAP_FACTORY = new IntFunction() {
            @Override
            public SetMultimap apply(int len) {
                return new SetMultimap(N.initHashCapacity(len));
            }
        };

        private Factory() {
            // singleton.
        }

        public static IntFunction ofBooleanArray() {
            return BOOLEAN_ARRAY;
        }

        public static IntFunction ofCharArray() {
            return CHAR_ARRAY;
        }

        public static IntFunction ofByteArray() {
            return BYTE_ARRAY;
        }

        public static IntFunction ofShortArray() {
            return SHORT_ARRAY;
        }

        public static IntFunction ofIntArray() {
            return INT_ARRAY;
        }

        public static IntFunction ofLongArray() {
            return LONG_ARRAY;
        }

        public static IntFunction ofFloatArray() {
            return FLOAT_ARRAY;
        }

        public static IntFunction ofDoubleArray() {
            return DOUBLE_ARRAY;
        }

        public static IntFunction ofStringArray() {
            return STRING_ARRAY;
        }

        public static IntFunction ofObjectArray() {
            return OBJECT_ARRAY;
        }

        public static IntFunction ofBooleanList() {
            return BOOLEAN_LIST;
        }

        public static IntFunction ofCharList() {
            return CHAR_LIST;
        }

        public static IntFunction ofByteList() {
            return BYTE_LIST;
        }

        public static IntFunction ofShortList() {
            return SHORT_LIST;
        }

        public static IntFunction ofIntList() {
            return INT_LIST;
        }

        public static IntFunction ofLongList() {
            return LONG_LIST;
        }

        public static IntFunction ofFloatList() {
            return FLOAT_LIST;
        }

        public static IntFunction ofDoubleList() {
            return DOUBLE_LIST;
        }

        @SuppressWarnings("rawtypes")
        public static  IntFunction> ofList() {
            return (IntFunction) LIST_FACTORY;
        }

        @SuppressWarnings("rawtypes")
        public static  IntFunction> ofLinkedList() {
            return (IntFunction) LINKED_LIST_FACTORY;
        }

        @SuppressWarnings("rawtypes")
        public static  IntFunction> ofSet() {
            return (IntFunction) SET_FACTORY;
        }

        @SuppressWarnings("rawtypes")
        public static  IntFunction> ofLinkedHashSet() {
            return (IntFunction) LINKED_HASH_SET_FACTORY;
        }

        @SuppressWarnings("rawtypes")
        public static  IntFunction> ofSortedSet() {
            return (IntFunction) TREE_SET_FACTORY;
        }

        @SuppressWarnings("rawtypes")
        public static  IntFunction> ofNavigableSet() {
            return (IntFunction) TREE_SET_FACTORY;
        }

        @SuppressWarnings("rawtypes")
        public static  IntFunction> ofTreeSet() {
            return (IntFunction) TREE_SET_FACTORY;
        }

        @SuppressWarnings("rawtypes")
        public static  IntFunction> ofQueue() {
            return (IntFunction) QUEUE_FACTORY;
        }

        @SuppressWarnings("rawtypes")
        public static  IntFunction> ofDeque() {
            return (IntFunction) DEQUE_FACTORY;
        }

        @SuppressWarnings("rawtypes")
        public static  IntFunction> ofArrayDeque() {
            return (IntFunction) ARRAY_DEQUE_FACTORY;
        }

        @SuppressWarnings("rawtypes")
        public static  IntFunction> ofLinkedBlockingQueue() {
            return (IntFunction) LINKED_BLOCKING_QUEUE_FACTORY;
        }

        @SuppressWarnings("rawtypes")
        public static  IntFunction> ofConcurrentLinkedQueue() {
            return (IntFunction) CONCURRENT_LINKED_QUEUE_FACTORY;
        }

        @SuppressWarnings("rawtypes")
        public static  IntFunction> ofPriorityQueue() {
            return (IntFunction) PRIORITY_QUEUE_FACTORY;
        }

        @SuppressWarnings("rawtypes")
        public static  IntFunction> ofMap() {
            return (IntFunction) MAP_FACTORY;
        }

        @SuppressWarnings("rawtypes")
        public static  IntFunction> ofLinkedHashMap() {
            return (IntFunction) LINKED_HASH_MAP_FACTORY;
        }

        @SuppressWarnings("rawtypes")
        public static  IntFunction> ofIdentityHashMap() {
            return (IntFunction) IDENTITY_HASH_MAP_FACTORY;
        }

        @SuppressWarnings("rawtypes")
        public static  IntFunction> ofSortedMap() {
            return (IntFunction) TREE_MAP_FACTORY;
        }

        @SuppressWarnings("rawtypes")
        public static  IntFunction> ofNavigableMap() {
            return (IntFunction) TREE_MAP_FACTORY;
        }

        @SuppressWarnings("rawtypes")
        public static  IntFunction> ofTreeMap() {
            return (IntFunction) TREE_MAP_FACTORY;
        }

        @SuppressWarnings("rawtypes")
        public static  IntFunction> ofConcurrentMap() {
            return (IntFunction) CONCURRENT_HASH_MAP_FACTORY;
        }

        @SuppressWarnings("rawtypes")
        public static  IntFunction> ofConcurrentHashMap() {
            return (IntFunction) CONCURRENT_HASH_MAP_FACTORY;
        }

        @SuppressWarnings("rawtypes")
        public static  IntFunction> ofBiMap() {
            return (IntFunction) BI_MAP_FACTORY;
        }

        @SuppressWarnings("rawtypes")
        public static  IntFunction> ofMultiset() {
            return (IntFunction) MULTISET_FACTORY;
        }

        @SuppressWarnings("rawtypes")
        public static  IntFunction> ofLongMultiset() {
            return (IntFunction) LONG_MULTISET_FACTORY;
        }

        @SuppressWarnings("rawtypes")
        public static  IntFunction> ofListMultimap() {
            return (IntFunction) LIST_MULTIMAP_FACTORY;
        }

        @SuppressWarnings("rawtypes")
        public static  IntFunction> ofSetMultimap() {
            return (IntFunction) SET_MULTIMAP_FACTORY;
        }

        /**
         * Won't work.
         * 
         * @return
         * @throws UnsupportedOperationException
         * 
         */
        @Deprecated
        public static IntFunction> ofImmutableList() {
            throw new UnsupportedOperationException();
        }

        /**
         * Won't work.
         * 
         * @return
         * @throws UnsupportedOperationException
         * 
         */
        @Deprecated
        public static IntFunction> ofImmutableSet() {
            throw new UnsupportedOperationException();
        }

        /**
         * Won't work.
         * 
         * @return
         * @throws UnsupportedOperationException
         * 
         */
        @Deprecated
        public static IntFunction> ofImmutableMap() {
            throw new UnsupportedOperationException();
        }

        public static final class IntFunctions extends Factory {
            private IntFunctions() {
                // singleton.
            }
        }
    }

    public static final class Suppliers {
        private static final Supplier UUID = new Supplier() {
            @Override
            public String get() {
                return N.uuid();
            }
        };

        private static final Supplier GUID = new Supplier() {
            @Override
            public String get() {
                return N.guid();
            }
        };

        private static final Supplier EMPTY_BOOLEAN_ARRAY = new Supplier() {
            @Override
            public boolean[] get() {
                return N.EMPTY_BOOLEAN_ARRAY;
            }
        };

        private static final Supplier EMPTY_CHAR_ARRAY = new Supplier() {
            @Override
            public char[] get() {
                return N.EMPTY_CHAR_ARRAY;
            }
        };

        private static final Supplier EMPTY_BYTE_ARRAY = new Supplier() {
            @Override
            public byte[] get() {
                return N.EMPTY_BYTE_ARRAY;
            }
        };

        private static final Supplier EMPTY_SHORT_ARRAY = new Supplier() {
            @Override
            public short[] get() {
                return N.EMPTY_SHORT_ARRAY;
            }
        };

        private static final Supplier EMPTY_INT_ARRAY = new Supplier() {
            @Override
            public int[] get() {
                return N.EMPTY_INT_ARRAY;
            }
        };

        private static final Supplier EMPTY_LONG_ARRAY = new Supplier() {
            @Override
            public long[] get() {
                return N.EMPTY_LONG_ARRAY;
            }
        };

        private static final Supplier EMPTY_FLOAT_ARRAY = new Supplier() {
            @Override
            public float[] get() {
                return N.EMPTY_FLOAT_ARRAY;
            }
        };

        private static final Supplier EMPTY_DOUBLE_ARRAY = new Supplier() {
            @Override
            public double[] get() {
                return N.EMPTY_DOUBLE_ARRAY;
            }
        };

        private static final Supplier EMPTY_STRING_ARRAY = new Supplier() {
            @Override
            public String[] get() {
                return N.EMPTY_STRING_ARRAY;
            }
        };

        private static final Supplier EMPTY_OBJECT_ARRAY = new Supplier() {
            @Override
            public Object[] get() {
                return N.EMPTY_OBJECT_ARRAY;
            }
        };

        private static final Supplier BOOLEAN_LIST = new Supplier() {
            @Override
            public BooleanList get() {
                return new BooleanList();
            }
        };

        private static final Supplier CHAR_LIST = new Supplier() {
            @Override
            public CharList get() {
                return new CharList();
            }
        };

        private static final Supplier BYTE_LIST = new Supplier() {
            @Override
            public ByteList get() {
                return new ByteList();
            }
        };

        private static final Supplier SHORT_LIST = new Supplier() {
            @Override
            public ShortList get() {
                return new ShortList();
            }
        };

        private static final Supplier INT_LIST = new Supplier() {
            @Override
            public IntList get() {
                return new IntList();
            }
        };

        private static final Supplier LONG_LIST = new Supplier() {
            @Override
            public LongList get() {
                return new LongList();
            }
        };

        private static final Supplier FLOAT_LIST = new Supplier() {
            @Override
            public FloatList get() {
                return new FloatList();
            }
        };

        private static final Supplier DOUBLE_LIST = new Supplier() {
            @Override
            public DoubleList get() {
                return new DoubleList();
            }
        };

        @SuppressWarnings("rawtypes")
        private static final Supplier LIST = new Supplier() {
            @Override
            public List get() {
                return new ArrayList();
            }
        };

        @SuppressWarnings("rawtypes")
        private static final Supplier LINKED_LIST = new Supplier() {
            @Override
            public LinkedList get() {
                return new LinkedList();
            }
        };

        @SuppressWarnings("rawtypes")
        private static final Supplier SET = new Supplier() {
            @Override
            public Set get() {
                return new HashSet();
            }
        };

        @SuppressWarnings("rawtypes")
        private static final Supplier LINKED_HASH_SET = new Supplier() {
            @Override
            public LinkedHashSet get() {
                return new LinkedHashSet();
            }
        };

        @SuppressWarnings("rawtypes")
        private static final Supplier TREE_SET = new Supplier() {
            @Override
            public TreeSet get() {
                return new TreeSet();
            }
        };

        @SuppressWarnings("rawtypes")
        private static final Supplier QUEUE = new Supplier() {
            @Override
            public Queue get() {
                return new LinkedList();
            }
        };

        @SuppressWarnings("rawtypes")
        private static final Supplier DEQUE = new Supplier() {
            @Override
            public Deque get() {
                return new LinkedList();
            }
        };

        @SuppressWarnings("rawtypes")
        private static final Supplier ARRAY_DEQUE = new Supplier() {
            @Override
            public ArrayDeque get() {
                return new ArrayDeque();
            }
        };

        @SuppressWarnings("rawtypes")
        private static final Supplier LINKED_BLOCKING_QUEUE = new Supplier() {
            @Override
            public LinkedBlockingQueue get() {
                return new LinkedBlockingQueue();
            }
        };

        @SuppressWarnings("rawtypes")
        private static final Supplier CONCURRENT_LINKED_QUEUE = new Supplier() {
            @Override
            public ConcurrentLinkedQueue get() {
                return new ConcurrentLinkedQueue();
            }
        };

        @SuppressWarnings("rawtypes")
        private static final Supplier PRIORITY_QUEUE = new Supplier() {
            @Override
            public PriorityQueue get() {
                return new PriorityQueue();
            }
        };

        @SuppressWarnings("rawtypes")
        private static final Supplier MAP = new Supplier() {
            @Override
            public Map get() {
                return new HashMap();
            }
        };

        @SuppressWarnings("rawtypes")
        private static final Supplier LINKED_HASH_MAP = new Supplier() {
            @Override
            public LinkedHashMap get() {
                return new LinkedHashMap();
            }
        };

        @SuppressWarnings("rawtypes")
        private static final Supplier IDENTITY_HASH_MAP = new Supplier() {
            @Override
            public IdentityHashMap get() {
                return new IdentityHashMap();
            }
        };

        @SuppressWarnings("rawtypes")
        private static final Supplier TREE_MAP = new Supplier() {
            @Override
            public TreeMap get() {
                return new TreeMap();
            }
        };

        @SuppressWarnings("rawtypes")
        private static final Supplier CONCURRENT_HASH_MAP = new Supplier() {
            @Override
            public ConcurrentHashMap get() {
                return new ConcurrentHashMap();
            }
        };

        @SuppressWarnings("rawtypes")
        private static final Supplier BI_MAP = new Supplier() {
            @Override
            public BiMap get() {
                return new BiMap();
            }
        };

        @SuppressWarnings("rawtypes")
        private static final Supplier MULTISET = new Supplier() {
            @Override
            public Multiset get() {
                return new Multiset();
            }
        };

        @SuppressWarnings("rawtypes")
        private static final Supplier LONG_MULTISET = new Supplier() {
            @Override
            public LongMultiset get() {
                return new LongMultiset();
            }
        };

        @SuppressWarnings("rawtypes")
        private static final Supplier LIST_MULTIMAP = new Supplier() {
            @Override
            public ListMultimap get() {
                return N.newListMultimap();
            }
        };

        @SuppressWarnings("rawtypes")
        private static final Supplier SET_MULTIMAP = new Supplier() {
            @Override
            public SetMultimap get() {
                return N.newSetMultimap();
            }
        };

        private static final Supplier STRING_BUILDER = new Supplier() {
            @Override
            public StringBuilder get() {
                return new StringBuilder();
            }
        };

        private Suppliers() {
            // singleton.
        }

        public static Supplier ofUUID() {
            return UUID;
        }

        public static Supplier ofGUID() {
            return GUID;
        }

        public static Supplier ofEmptyBooleanArray() {
            return EMPTY_BOOLEAN_ARRAY;
        }

        public static Supplier ofEmptyCharArray() {
            return EMPTY_CHAR_ARRAY;
        }

        public static Supplier ofEmptyByteArray() {
            return EMPTY_BYTE_ARRAY;
        }

        public static Supplier ofEmptyShortArray() {
            return EMPTY_SHORT_ARRAY;
        }

        public static Supplier ofEmptyIntArray() {
            return EMPTY_INT_ARRAY;
        }

        public static Supplier ofEmptyLongArray() {
            return EMPTY_LONG_ARRAY;
        }

        public static Supplier ofEmptyFloatArray() {
            return EMPTY_FLOAT_ARRAY;
        }

        public static Supplier ofEmptyDoubleArray() {
            return EMPTY_DOUBLE_ARRAY;
        }

        public static Supplier ofEmptyStringArray() {
            return EMPTY_STRING_ARRAY;
        }

        public static Supplier ofEmptyObjectArray() {
            return EMPTY_OBJECT_ARRAY;
        }

        public static Supplier ofBooleanList() {
            return BOOLEAN_LIST;
        }

        public static Supplier ofCharList() {
            return CHAR_LIST;
        }

        public static Supplier ofByteList() {
            return BYTE_LIST;
        }

        public static Supplier ofShortList() {
            return SHORT_LIST;
        }

        public static Supplier ofIntList() {
            return INT_LIST;
        }

        public static Supplier ofLongList() {
            return LONG_LIST;
        }

        public static Supplier ofFloatList() {
            return FLOAT_LIST;
        }

        public static Supplier ofDoubleList() {
            return DOUBLE_LIST;
        }

        @SuppressWarnings("rawtypes")
        public static  Supplier> ofList() {
            return (Supplier) LIST;
        }

        @SuppressWarnings("rawtypes")
        public static  Supplier> ofLinkedList() {
            return (Supplier) LINKED_LIST;
        }

        @SuppressWarnings("rawtypes")
        public static  Supplier> ofSet() {
            return (Supplier) SET;
        }

        @SuppressWarnings("rawtypes")
        public static  Supplier> ofLinkedHashSet() {
            return (Supplier) LINKED_HASH_SET;
        }

        @SuppressWarnings("rawtypes")
        public static  Supplier> ofSortedSet() {
            return (Supplier) TREE_SET;
        }

        @SuppressWarnings("rawtypes")
        public static  Supplier> ofNavigableSet() {
            return (Supplier) TREE_SET;
        }

        @SuppressWarnings("rawtypes")
        public static  Supplier> ofTreeSet() {
            return (Supplier) TREE_SET;
        }

        @SuppressWarnings("rawtypes")
        public static  Supplier> ofQueue() {
            return (Supplier) QUEUE;
        }

        @SuppressWarnings("rawtypes")
        public static  Supplier> ofDeque() {
            return (Supplier) DEQUE;
        }

        @SuppressWarnings("rawtypes")
        public static  Supplier> ofArrayDeque() {
            return (Supplier) ARRAY_DEQUE;
        }

        @SuppressWarnings("rawtypes")
        public static  Supplier> ofLinkedBlockingQueue() {
            return (Supplier) LINKED_BLOCKING_QUEUE;
        }

        @SuppressWarnings("rawtypes")
        public static  Supplier> ofConcurrentLinkedQueue() {
            return (Supplier) CONCURRENT_LINKED_QUEUE;
        }

        @SuppressWarnings("rawtypes")
        public static  Supplier> ofPriorityQueue() {
            return (Supplier) PRIORITY_QUEUE;
        }

        @SuppressWarnings("rawtypes")
        public static  Supplier> ofMap() {
            return (Supplier) MAP;
        }

        @SuppressWarnings("rawtypes")
        public static  Supplier> ofLinkedHashMap() {
            return (Supplier) LINKED_HASH_MAP;
        }

        @SuppressWarnings("rawtypes")
        public static  Supplier> ofIdentityHashMap() {
            return (Supplier) IDENTITY_HASH_MAP;
        }

        @SuppressWarnings("rawtypes")
        public static  Supplier> ofSortedMap() {
            return (Supplier) TREE_MAP;
        }

        @SuppressWarnings("rawtypes")
        public static  Supplier> ofNavigableMap() {
            return (Supplier) TREE_MAP;
        }

        @SuppressWarnings("rawtypes")
        public static  Supplier> ofTreeMap() {
            return (Supplier) TREE_MAP;
        }

        @SuppressWarnings("rawtypes")
        public static  Supplier> ofConcurrentMap() {
            return (Supplier) CONCURRENT_HASH_MAP;
        }

        @SuppressWarnings("rawtypes")
        public static  Supplier> ofConcurrentHashMap() {
            return (Supplier) CONCURRENT_HASH_MAP;
        }

        @SuppressWarnings("rawtypes")
        public static  Supplier> ofBiMap() {
            return (Supplier) BI_MAP;
        }

        @SuppressWarnings("rawtypes")
        public static  Supplier> ofMultiset() {
            return (Supplier) MULTISET;
        }

        @SuppressWarnings("rawtypes")
        public static  Supplier> ofLongMultiset() {
            return (Supplier) LONG_MULTISET;
        }

        @SuppressWarnings("rawtypes")
        public static  Supplier> ofListMultimap() {
            return (Supplier) LIST_MULTIMAP;
        }

        @SuppressWarnings("rawtypes")
        public static  Supplier> ofSetMultimap() {
            return (Supplier) SET_MULTIMAP;
        }

        public static Supplier ofStringBuilder() {
            return STRING_BUILDER;
        }

        /**
         * Won't work.
         * 
         * @return
         * @throws UnsupportedOperationException
         * 
         */
        @Deprecated
        public static Supplier> ofImmutableList() {
            throw new UnsupportedOperationException();
        }

        /**
         * Won't work.
         * 
         * @return
         * @throws UnsupportedOperationException
         * 
         */
        @Deprecated
        public static Supplier> ofImmutableSet() {
            throw new UnsupportedOperationException();
        }

        /**
         * Won't work.
         * 
         * @return
         * @throws UnsupportedOperationException
         * 
         */
        @Deprecated
        public static Supplier> ofImmutableMap() {
            throw new UnsupportedOperationException();
        }
    }

    public static final class Predicates {

        private Predicates() {
            // singleton.
        }

        public static  Predicate create(final U u, final BiPredicate predicate) {
            N.checkArgNotNull(predicate);

            return new Predicate() {
                @Override
                public boolean test(T t) {
                    return predicate.test(t, u);
                }
            };
        }

        public static  Predicate indexed(final IndexedPredicate predicate) {
            N.checkArgNotNull(predicate);

            return new Predicate() {
                private final MutableInt idx = new MutableInt(0);

                @Override
                public boolean test(T t) {
                    return predicate.test(idx.getAndIncrement(), t);
                }
            };
        }

        public static  Predicate distinct() {
            return new Predicate() {
                private final Set set = new HashSet();

                @Override
                public boolean test(T value) {
                    return set.add(value);
                }
            };
        }

        public static  Predicate distinctBy(final Function mapper) {
            return new Predicate() {
                private final Set set = new HashSet();

                @Override
                public boolean test(T value) {
                    return set.add(mapper.apply(value));
                }
            };
        }

        public static  Predicate concurrentDistinct() {
            return new Predicate() {
                private final Map map = new ConcurrentHashMap<>();

                @Override
                public boolean test(T value) {
                    return map.put(value, N.NULL_MASK) == null;
                }
            };
        }

        public static  Predicate concurrentDistinctBy(final Function mapper) {
            return new Predicate() {
                private final Map map = new ConcurrentHashMap<>();

                @Override
                public boolean test(T value) {
                    return map.put(mapper.apply(value), N.NULL_MASK) == null;
                }
            };
        }

        /**
         * Remove the continuous repeat elements.
         * Returns a stateful predicate which should not be used in parallel stream.
         * 
         * @return
         */
        public static  Predicate skipRepeats() {
            return new Predicate() {
                private T pre = (T) NULL;

                @Override
                public boolean test(T value) {
                    boolean res = pre == NULL || N.equals(value, pre) == false;
                    pre = value;
                    return res;
                }
            };
        }
    }

    public static final class BiPredicates {

        @SuppressWarnings("rawtypes")
        private static final BiPredicate ALWAYS_TRUE = new BiPredicate() {
            @Override
            public boolean test(Object t, Object u) {
                return true;
            }
        };

        @SuppressWarnings("rawtypes")
        private static final BiPredicate ALWAYS_FALSE = new BiPredicate() {
            @Override
            public boolean test(Object t, Object u) {
                return false;
            }
        };

        @SuppressWarnings("rawtypes")
        private static final BiPredicate EQUAL = new BiPredicate() {
            @Override
            public boolean test(Object t, Object u) {
                return N.equals(t, u);
            }
        };

        @SuppressWarnings("rawtypes")
        private static final BiPredicate NOT_EQUAL = new BiPredicate() {
            @Override
            public boolean test(Object t, Object u) {
                return !N.equals(t, u);
            }
        };

        @SuppressWarnings("rawtypes")
        private static final BiPredicate GREATER_THAN = new BiPredicate() {
            @Override
            public boolean test(Comparable t, Comparable u) {
                return N.compare(t, u) > 0;
            }
        };

        @SuppressWarnings("rawtypes")
        private static final BiPredicate GREATER_EQUAL = new BiPredicate() {
            @Override
            public boolean test(Comparable t, Comparable u) {
                return N.compare(t, u) >= 0;
            }
        };

        @SuppressWarnings("rawtypes")
        private static final BiPredicate LESS_THAN = new BiPredicate() {
            @Override
            public boolean test(Comparable t, Comparable u) {
                return N.compare(t, u) < 0;
            }
        };

        @SuppressWarnings("rawtypes")
        private static final BiPredicate LESS_EQUAL = new BiPredicate() {
            @Override
            public boolean test(Comparable t, Comparable u) {
                return N.compare(t, u) <= 0;
            }
        };

        private BiPredicates() {
            // singleton.
        }

        public static  BiPredicate alwaysTrue() {
            return ALWAYS_TRUE;
        }

        public static  BiPredicate alwaysFalse() {
            return ALWAYS_FALSE;
        }

        public static  BiPredicate indexed(final IndexedBiPredicate predicate) {
            N.checkArgNotNull(predicate);

            return new BiPredicate() {
                private final MutableInt idx = new MutableInt(0);

                @Override
                public boolean test(U u, T t) {
                    return predicate.test(u, idx.getAndIncrement(), t);
                }
            };
        }
    }

    public static final class TriPredicates {

        @SuppressWarnings("rawtypes")
        private static final TriPredicate ALWAYS_TRUE = new TriPredicate() {
            @Override
            public boolean test(Object a, Object b, Object c) {
                return true;
            }
        };

        @SuppressWarnings("rawtypes")
        private static final TriPredicate ALWAYS_FALSE = new TriPredicate() {
            @Override
            public boolean test(Object a, Object b, Object c) {
                return false;
            }
        };

        private TriPredicates() {
            // singleton.
        }

        public static  TriPredicate alwaysTrue() {
            return ALWAYS_TRUE;
        }

        public static  TriPredicate alwaysFalse() {
            return ALWAYS_FALSE;
        }

    }

    public static final class Consumers {

        private Consumers() {
            // singleton.
        }

        public static  Consumer create(final U u, final BiConsumer action) {
            N.checkArgNotNull(action);

            return new Consumer() {
                @Override
                public void accept(T t) {
                    action.accept(t, u);
                }
            };
        }

        /**
         * Returns a Consumer which calls the specified func.
         * 
         * @param func
         * @return
         */
        public static  Consumer create(final Function func) {
            N.checkArgNotNull(func);

            return new Consumer() {
                @Override
                public void accept(T t) {
                    func.apply(t);
                }
            };
        }

        public static  Consumer indexed(final IndexedConsumer action) {
            N.checkArgNotNull(action);

            return new Consumer() {
                private final MutableInt idx = new MutableInt(0);

                @Override
                public void accept(T t) {
                    action.accept(idx.getAndIncrement(), t);
                }
            };
        }
    }

    public static final class BiConsumers {

        @SuppressWarnings("rawtypes")
        private static final BiConsumer DO_NOTHING = new BiConsumer() {
            @Override
            public void accept(Object t, Object u) {
                // do nothing.
            }
        };

        private static final BiConsumer, Object> ADD = new BiConsumer, Object>() {
            @Override
            public void accept(Collection t, Object u) {
                t.add(u);
            }
        };

        private static final BiConsumer, Collection> ADD_ALL = new BiConsumer, Collection>() {
            @Override
            public void accept(Collection t, Collection u) {
                t.addAll(u);
            }
        };

        @SuppressWarnings("rawtypes")
        private static final BiConsumer ADD_ALL_2 = new BiConsumer() {
            @Override
            public void accept(PrimitiveList t, PrimitiveList u) {
                t.addAll(u);
            }
        };

        private static final BiConsumer, Object> REMOVE = new BiConsumer, Object>() {
            @Override
            public void accept(Collection t, Object u) {
                t.remove(u);
            }
        };

        private static final BiConsumer, Collection> REMOVE_ALL = new BiConsumer, Collection>() {
            @Override
            public void accept(Collection t, Collection u) {
                t.removeAll(u);
            }
        };

        @SuppressWarnings("rawtypes")
        private static final BiConsumer REMOVE_ALL_2 = new BiConsumer() {
            @Override
            public void accept(PrimitiveList t, PrimitiveList u) {
                t.removeAll(u);
            }
        };

        private static final BiConsumer, Map.Entry> PUT = new BiConsumer, Map.Entry>() {
            @Override
            public void accept(Map t, Map.Entry u) {
                t.put(u.getKey(), u.getValue());
            }
        };

        private static final BiConsumer, Map> PUT_ALL = new BiConsumer, Map>() {
            @Override
            public void accept(Map t, Map u) {
                t.putAll(u);
            }
        };

        private static final BiConsumer, Object> REMOVE_BY_KEY = new BiConsumer, Object>() {
            @Override
            public void accept(Map t, Object u) {
                t.remove(u);
            }
        };

        private static final BiConsumer MERGE = new BiConsumer() {
            @Override
            public void accept(Joiner t, Joiner u) {
                t.merge(u);
            }
        };

        private static final BiConsumer APPEND = new BiConsumer() {
            @Override
            public void accept(StringBuilder t, Object u) {
                t.append(u);
            }
        };

        private BiConsumers() {
            // singleton.
        }

        public static  BiConsumer doNothing() {
            return DO_NOTHING;
        }

        public static > BiConsumer ofAdd() {
            return (BiConsumer) ADD;
        }

        public static > BiConsumer ofAddAll() {
            return (BiConsumer) ADD_ALL;
        }

        @SuppressWarnings("rawtypes")
        public static  BiConsumer ofAddAlll() {
            return (BiConsumer) ADD_ALL_2;
        }

        public static > BiConsumer ofRemove() {
            return (BiConsumer) REMOVE;
        }

        public static > BiConsumer ofRemoveAll() {
            return (BiConsumer) REMOVE_ALL;
        }

        @SuppressWarnings("rawtypes")
        public static  BiConsumer ofRemoveAlll() {
            return (BiConsumer) REMOVE_ALL_2;
        }

        public static , E extends Map.Entry> BiConsumer ofPut() {
            return (BiConsumer) PUT;
        }

        public static > BiConsumer ofPutAll() {
            return (BiConsumer) PUT_ALL;
        }

        public static > BiConsumer ofRemoveByKey() {
            return (BiConsumer) REMOVE_BY_KEY;
        }

        public static BiConsumer ofMerge() {
            return MERGE;
        }

        public static  BiConsumer ofAppend() {
            return (BiConsumer) APPEND;
        }

        /**
         * Returns a BiConsumer which calls the specified func.
         * 
         * @param func
         * @return
         */
        public static  BiConsumer create(final BiFunction func) {
            N.checkArgNotNull(func);

            return new BiConsumer() {
                @Override
                public void accept(T t, U u) {
                    func.apply(t, u);
                }
            };
        }

        public static  BiConsumer indexed(final IndexedBiConsumer action) {
            N.checkArgNotNull(action);

            return new BiConsumer() {
                private final MutableInt idx = new MutableInt(0);

                @Override
                public void accept(U u, T t) {
                    action.accept(u, idx.getAndIncrement(), t);
                }
            };
        }
    }

    public static final class TriConsumers {
        private TriConsumers() {
            // singleton.
        }

        /**
         * Returns a TriConsumer which calls the specified func.
         * 
         * @param func
         * @return
         */
        public static  TriConsumer create(final TriFunction func) {
            N.checkArgNotNull(func);

            return new TriConsumer() {
                @Override
                public void accept(A a, B b, C c) {
                    func.apply(a, b, c);
                }
            };
        }
    }

    public static final class Functions {
        private Functions() {
            // singleton.
        }

        public static  Function create(final U u, final BiFunction func) {
            N.checkArgNotNull(func);

            return new Function() {
                @Override
                public R apply(T t) {
                    return func.apply(t, u);
                }
            };
        }

        /**
         * Returns a Function which calls the specified action and always return an emptyOptional if action is executed successfully.
         * 
         * @param action
         * @return
         */
        public static  Function> create(final Consumer action) {
            N.checkArgNotNull(action);

            return new Function>() {
                @Override
                public Optional apply(T t) {
                    action.accept(t);
                    return Optional.empty();
                }
            };
        }

        public static  Function indexed(final IndexedFunction func) {
            N.checkArgNotNull(func);

            return new Function() {
                private final MutableInt idx = new MutableInt(0);

                @Override
                public R apply(T t) {
                    return func.apply(idx.getAndIncrement(), t);
                }
            };
        }

        /**
         * 
         * @return
         * @deprecated replaced by PairFn#toList();
         */
        @Deprecated
        public static  Function, List> pairToList() {
            return Pairs.toList();
        }

        /**
         * 
         * @return
         * @deprecated replaced by PairFn#toSet();
         */
        @Deprecated
        public static  Function, Set> pairToSet() {
            return Pairs.toSet();
        }

        /**
         * 
         * @return
         * @deprecated replaced by TripleFn#toList();
         */
        @Deprecated
        public static  Function, List> tripleToList() {
            return Triples.toList();
        }

        /**
         * 
         * @deprecated replaced by TripleFn#toSet();
         */
        @Deprecated
        public static  Function, Set> tripleToSet() {
            return Triples.toSet();
        }
    }

    public static final class BiFunctions {

        private static final BiFunction RETURN_FIRST = new BiFunction() {
            @Override
            public Object apply(Object t, Object u) {
                return t;
            }
        };

        private static final BiFunction RETURN_SECOND = new BiFunction() {
            @Override
            public Object apply(Object t, Object u) {
                return u;
            }
        };

        private static final BiFunction, Object, Collection> ADD = new BiFunction, Object, Collection>() {
            @Override
            public Collection apply(Collection t, Object u) {
                t.add(u);
                return t;
            }
        };

        private static final BiFunction, Collection, Collection> ADD_ALL = new BiFunction, Collection, Collection>() {
            @Override
            public Collection apply(Collection t, Collection u) {
                t.addAll(u);
                return t;
            }
        };

        @SuppressWarnings("rawtypes")
        private static final BiFunction ADD_ALL_2 = new BiFunction() {
            @Override
            public PrimitiveList apply(PrimitiveList t, PrimitiveList u) {
                t.addAll(u);
                return t;
            }
        };

        private static final BiFunction, Object, Collection> REMOVE = new BiFunction, Object, Collection>() {
            @Override
            public Collection apply(Collection t, Object u) {
                t.remove(u);
                return t;
            }
        };

        private static final BiFunction, Collection, Collection> REMOVE_ALL = new BiFunction, Collection, Collection>() {
            @Override
            public Collection apply(Collection t, Collection u) {
                t.removeAll(u);
                return t;
            }
        };

        @SuppressWarnings("rawtypes")
        private static final BiFunction REMOVE_ALL_2 = new BiFunction() {
            @Override
            public PrimitiveList apply(PrimitiveList t, PrimitiveList u) {
                t.removeAll(u);
                return t;
            }
        };

        private static final BiFunction, Map.Entry, Map> PUT = new BiFunction, Map.Entry, Map>() {
            @Override
            public Map apply(Map t, Map.Entry u) {
                t.put(u.getKey(), u.getValue());
                return t;
            }
        };

        private static final BiFunction, Map, Map> PUT_ALL = new BiFunction, Map, Map>() {
            @Override
            public Map apply(Map t, Map u) {
                t.putAll(u);
                return t;
            }
        };

        private static final BiFunction, Object, Map> REMOVE_BY_KEY = new BiFunction, Object, Map>() {
            @Override
            public Map apply(Map t, Object u) {
                t.remove(u);
                return t;
            }
        };

        private static final BiFunction MERGE = new BiFunction() {
            @Override
            public Joiner apply(Joiner t, Joiner u) {
                return t.merge(u);
            }
        };

        private static final BiFunction APPEND = new BiFunction() {
            @Override
            public StringBuilder apply(StringBuilder t, Object u) {
                return t.append(u);
            }
        };

        private BiFunctions() {
            // singleton.
        }

        public static  BiFunction returnFirst() {
            return (BiFunction) RETURN_FIRST;
        }

        public static  BiFunction returnSecond() {
            return (BiFunction) RETURN_SECOND;
        }

        public static > BiFunction ofAdd() {
            return (BiFunction) ADD;
        }

        public static > BiFunction ofAddAll() {
            return (BiFunction) ADD_ALL;
        }

        @SuppressWarnings("rawtypes")
        public static  BiFunction ofAddAlll() {
            return (BiFunction) ADD_ALL_2;
        }

        public static > BiFunction ofRemove() {
            return (BiFunction) REMOVE;
        }

        public static > BiFunction ofRemoveAll() {
            return (BiFunction) REMOVE_ALL;
        }

        @SuppressWarnings("rawtypes")
        public static  BiFunction ofRemoveAlll() {
            return (BiFunction) REMOVE_ALL_2;
        }

        public static , E extends Map.Entry> BiFunction ofPut() {
            return (BiFunction) PUT;
        }

        public static > BiFunction ofPutAll() {
            return (BiFunction) PUT_ALL;
        }

        public static , U> BiFunction ofRemoveByKey() {
            return (BiFunction) REMOVE_BY_KEY;
        }

        public static BiFunction ofMerge() {
            return MERGE;
        }

        public static  BiFunction ofAppend() {
            return (BiFunction) APPEND;
        }

        /**
         * Returns a BiFunction which calls the specified action and always return an emptyOptional if action is executed successfully.
         * 
         * @param action
         * @return
         */
        public static  BiFunction> create(final BiConsumer action) {
            N.checkArgNotNull(action);

            return new BiFunction>() {
                @Override
                public Optional apply(T t, U u) {
                    action.accept(t, u);
                    return Optional.empty();
                }
            };
        }

        public static  BiFunction indexed(final IndexedBiFunction func) {
            N.checkArgNotNull(func);

            return new BiFunction() {
                private final MutableInt idx = new MutableInt(0);

                @Override
                public R apply(U u, T t) {
                    return func.apply(u, idx.getAndIncrement(), t);
                }
            };
        }
    }

    public static final class TriFunctions {

        private TriFunctions() {
            // singleton.
        }

        /**
         * Returns a TriFunction which calls the specified action and always return an emptyOptional if action is executed successfully.
         * 
         * @param action
         * @return
         */
        public static  TriFunction> create(final TriConsumer action) {
            N.checkArgNotNull(action);

            return new TriFunction>() {
                @Override
                public Optional apply(A a, B b, C c) {
                    action.accept(a, b, c);
                    return Optional.empty();
                }
            };
        }
    }

    public static final class BinaryOperators {

        @SuppressWarnings("rawtypes")
        private static final BinaryOperator THROWING_MERGER = new BinaryOperator() {
            @Override
            public Object apply(Object t, Object u) {
                throw new IllegalStateException(String.format("Duplicate key (attempted merging values %s and %s)", t, u));
            }
        };

        @SuppressWarnings("rawtypes")
        private static final BinaryOperator IGNORING_MERGER = new BinaryOperator() {
            @Override
            public Object apply(Object t, Object u) {
                return t;
            }
        };

        @SuppressWarnings("rawtypes")
        private static final BinaryOperator REPLACING_MERGER = new BinaryOperator() {
            @Override
            public Object apply(Object t, Object u) {
                return u;
            }
        };

        private static final BinaryOperator> ADD_ALL_TO_FIRST = new BinaryOperator>() {
            @Override
            public Collection apply(Collection t, Collection u) {
                t.addAll(u);
                return t;
            }
        };

        private static final BinaryOperator> ADD_ALL_TO_BIGGER = new BinaryOperator>() {
            @Override
            public Collection apply(Collection t, Collection u) {
                if (t.size() >= u.size()) {
                    t.addAll(u);
                    return t;
                } else {
                    u.addAll(t);
                    return u;
                }
            }
        };

        private static final BinaryOperator> REMOVE_ALL_FROM_FIRST = new BinaryOperator>() {
            @Override
            public Collection apply(Collection t, Collection u) {
                t.removeAll(u);
                return t;
            }
        };

        private static final BinaryOperator> PUT_ALL_TO_FIRST = new BinaryOperator>() {
            @Override
            public Map apply(Map t, Map u) {
                t.putAll(u);
                return t;
            }
        };

        private static final BinaryOperator> PUT_ALL_TO_BIGGER = new BinaryOperator>() {
            @Override
            public Map apply(Map t, Map u) {
                if (t.size() >= u.size()) {
                    t.putAll(u);
                    return t;
                } else {
                    u.putAll(t);
                    return u;
                }
            }
        };

        private static final BinaryOperator MERGE_TO_FIRST = new BinaryOperator() {
            @Override
            public Joiner apply(Joiner t, Joiner u) {
                return t.merge(u);
            }
        };

        private static final BinaryOperator MERGE_TO_BIGGER = new BinaryOperator() {
            @Override
            public Joiner apply(Joiner t, Joiner u) {
                if (t.length() >= u.length()) {
                    return t.merge(u);
                } else {
                    return u.merge(t);
                }
            }
        };

        private static final BinaryOperator APPEND_TO_FIRST = new BinaryOperator() {
            @Override
            public StringBuilder apply(StringBuilder t, StringBuilder u) {
                return t.append(u);
            }
        };

        private static final BinaryOperator APPEND_TO_BIGGER = new BinaryOperator() {
            @Override
            public StringBuilder apply(StringBuilder t, StringBuilder u) {
                if (t.length() >= u.length()) {
                    return t.append(u);
                } else {
                    return u.append(t);
                }
            }
        };

        private static final BinaryOperator CONCAT = new BinaryOperator() {
            @Override
            public String apply(String t, String u) {
                return t + u;
            }
        };

        private static final BinaryOperator ADD_INTEGER = new BinaryOperator() {
            @Override
            public Integer apply(Integer t, Integer u) {
                return t.intValue() + u.intValue();
            }
        };

        private static final BinaryOperator ADD_LONG = new BinaryOperator() {
            @Override
            public Long apply(Long t, Long u) {
                return t.longValue() + u.longValue();
            }
        };

        private static final BinaryOperator ADD_DOUBLE = new BinaryOperator() {
            @Override
            public Double apply(Double t, Double u) {
                return t.doubleValue() + u.doubleValue();
            }
        };

        private static final BinaryOperator ADD_BIG_INTEGER = new BinaryOperator() {
            @Override
            public BigInteger apply(BigInteger t, BigInteger u) {
                return t.add(u);
            }
        };

        private static final BinaryOperator ADD_BIG_DECIMAL = new BinaryOperator() {
            @Override
            public BigDecimal apply(BigDecimal t, BigDecimal u) {
                return t.add(u);
            }
        };

        @SuppressWarnings({ "rawtypes" })
        private static final BinaryOperator MIN = new BinaryOperator() {
            @Override
            public Comparable apply(Comparable t, Comparable u) {
                return N.compare(t, u) <= 0 ? t : u;
            }
        };

        @SuppressWarnings("rawtypes")
        private static final BinaryOperator MAX = new BinaryOperator() {
            @Override
            public Comparable apply(Comparable t, Comparable u) {
                return N.compare(t, u) >= 0 ? t : u;
            }
        };

        private BinaryOperators() {
            // singleton.
        }

        /**
         * 
         * @return
         * @deprecated replaced by {@code #ofAddAllToFirst()}
         */
        @Deprecated
        @SuppressWarnings("unchecked")
        public static > BinaryOperator ofAddAll() {
            return (BinaryOperator) ADD_ALL_TO_FIRST;
        }

        @SuppressWarnings("unchecked")
        public static > BinaryOperator ofAddAllToFirst() {
            return (BinaryOperator) ADD_ALL_TO_FIRST;
        }

        @SuppressWarnings("unchecked")
        public static > BinaryOperator ofAddAllToBigger() {
            return (BinaryOperator) ADD_ALL_TO_BIGGER;
        }

        /**
         * 
         * @return
         * @deprecated replaced by {@code #ofRemoveAllFromFirst()}.
         */
        @Deprecated
        @SuppressWarnings("unchecked")
        public static > BinaryOperator ofRemoveAll() {
            return (BinaryOperator) REMOVE_ALL_FROM_FIRST;
        }

        @SuppressWarnings("unchecked")
        public static > BinaryOperator ofRemoveAllFromFirst() {
            return (BinaryOperator) REMOVE_ALL_FROM_FIRST;
        }

        /**
         * 
         * @return
         * @deprecated replaced by {@code #ofPutAllToFirst()}
         */
        @Deprecated
        @SuppressWarnings("unchecked")
        public static > BinaryOperator ofPutAll() {
            return (BinaryOperator) PUT_ALL_TO_FIRST;
        }

        @SuppressWarnings("unchecked")
        public static > BinaryOperator ofPutAllToFirst() {
            return (BinaryOperator) PUT_ALL_TO_FIRST;
        }

        @SuppressWarnings("unchecked")
        public static > BinaryOperator ofPutAllToBigger() {
            return (BinaryOperator) PUT_ALL_TO_BIGGER;
        }

        /**
         * 
         * @return
         * @deprecated replaced by {@code #ofMergeToFirst}.
         */
        @Deprecated
        public static BinaryOperator ofMerge() {
            return MERGE_TO_FIRST;
        }

        public static BinaryOperator ofMergeToFirst() {
            return MERGE_TO_FIRST;
        }

        public static BinaryOperator ofMergeToBigger() {
            return MERGE_TO_BIGGER;
        }

        /**
         * 
         * @return
         * @deprecated replaced by {@code #ofAppendToFirst()}
         */
        @Deprecated
        public static BinaryOperator ofAppend() {
            return APPEND_TO_FIRST;
        }

        public static BinaryOperator ofAppendToFirst() {
            return APPEND_TO_FIRST;
        }

        public static BinaryOperator ofAppendToBigger() {
            return APPEND_TO_BIGGER;
        }

        public static BinaryOperator ofConcat() {
            return CONCAT;
        }

        public static BinaryOperator ofAddInt() {
            return ADD_INTEGER;
        }

        public static BinaryOperator ofAddLong() {
            return ADD_LONG;
        }

        public static BinaryOperator ofAddDouble() {
            return ADD_DOUBLE;
        }

        public static BinaryOperator ofAddBigInteger() {
            return ADD_BIG_INTEGER;
        }

        public static BinaryOperator ofAddBigDecimal() {
            return ADD_BIG_DECIMAL;
        }

        @SuppressWarnings({ "unchecked", "rawtypes" })
        public static > BinaryOperator min() {
            return (BinaryOperator) MIN;
        }

        @SuppressWarnings({ "unchecked", "rawtypes" })
        public static > BinaryOperator max() {
            return (BinaryOperator) MAX;
        }

        public static  BinaryOperator minBy(final Comparator comparator) {
            N.checkArgNotNull(comparator);

            return new BinaryOperator() {
                @Override
                public T apply(T t, T u) {
                    return comparator.compare(t, u) <= 0 ? t : u;
                }
            };
        }

        public static  BinaryOperator maxBy(final Comparator comparator) {
            N.checkArgNotNull(comparator);

            return new BinaryOperator() {
                @Override
                public T apply(T t, T u) {
                    return comparator.compare(t, u) >= 0 ? t : u;
                }
            };
        }
    }

    public static final class UnaryOperators {
        @SuppressWarnings("rawtypes")
        private static final UnaryOperator IDENTITY = new UnaryOperator() {
            @Override
            public Object apply(Object t) {
                return t;
            }
        };

        private UnaryOperators() {
            // singleton.
        }

        public static  UnaryOperator identity() {
            return IDENTITY;
        }
    }

    public static final class Ints {

        private static final IntPredicate POSITIVE = new IntPredicate() {
            @Override
            public boolean test(int t) {
                return t > 0;
            }
        };

        private static final IntPredicate NOT_NEGATIVE = new IntPredicate() {
            @Override
            public boolean test(int t) {
                return t >= 0;
            }
        };

        private static final IntBiPredicate EQUAL = new IntBiPredicate() {
            @Override
            public boolean test(int t, int u) {
                return t == u;
            }
        };

        private static final IntBiPredicate NOT_EQUAL = new IntBiPredicate() {
            @Override
            public boolean test(int t, int u) {
                return t != u;
            }
        };

        private static final IntBiPredicate GREATER_THAN = new IntBiPredicate() {
            @Override
            public boolean test(int t, int u) {
                return t > u;
            }
        };

        private static final IntBiPredicate GREATER_EQUAL = new IntBiPredicate() {
            @Override
            public boolean test(int t, int u) {
                return t >= u;
            }
        };

        private static final IntBiPredicate LESS_THAN = new IntBiPredicate() {
            @Override
            public boolean test(int t, int u) {
                return t < u;
            }
        };

        private static final IntBiPredicate LESS_EQUAL = new IntBiPredicate() {
            @Override
            public boolean test(int t, int u) {
                return t <= u;
            }
        };

        private Ints() {
            // Utility class.
        }

        public static IntPredicate positve() {
            return POSITIVE;
        }

        public static IntPredicate notNegative() {
            return NOT_NEGATIVE;
        }

        public static IntBiPredicate equal() {
            return EQUAL;
        }

        public static IntBiPredicate notEqual() {
            return NOT_EQUAL;
        }

        public static IntBiPredicate greaterThan() {
            return GREATER_THAN;
        }

        public static IntBiPredicate greaterEqual() {
            return GREATER_EQUAL;
        }

        public static IntBiPredicate lessThan() {
            return LESS_THAN;
        }

        public static IntBiPredicate lessEqual() {
            return LESS_EQUAL;
        }
    }

    public static final class Longs {

        private static final LongPredicate POSITIVE = new LongPredicate() {
            @Override
            public boolean test(long t) {
                return t > 0;
            }
        };

        private static final LongPredicate NOT_NEGATIVE = new LongPredicate() {
            @Override
            public boolean test(long t) {
                return t >= 0;
            }
        };

        private static final LongBiPredicate EQUAL = new LongBiPredicate() {
            @Override
            public boolean test(long t, long u) {
                return t == u;
            }
        };

        private static final LongBiPredicate NOT_EQUAL = new LongBiPredicate() {
            @Override
            public boolean test(long t, long u) {
                return t != u;
            }
        };

        private static final LongBiPredicate GREATER_THAN = new LongBiPredicate() {
            @Override
            public boolean test(long t, long u) {
                return t > u;
            }
        };

        private static final LongBiPredicate GREATER_EQUAL = new LongBiPredicate() {
            @Override
            public boolean test(long t, long u) {
                return t >= u;
            }
        };

        private static final LongBiPredicate LESS_THAN = new LongBiPredicate() {
            @Override
            public boolean test(long t, long u) {
                return t < u;
            }
        };

        private static final LongBiPredicate LESS_EQUAL = new LongBiPredicate() {
            @Override
            public boolean test(long t, long u) {
                return t <= u;
            }
        };

        private Longs() {
            // Utility class.
        }

        public static LongPredicate positve() {
            return POSITIVE;
        }

        public static LongPredicate notNegative() {
            return NOT_NEGATIVE;
        }

        public static LongBiPredicate equal() {
            return EQUAL;
        }

        public static LongBiPredicate notEqual() {
            return NOT_EQUAL;
        }

        public static LongBiPredicate greaterThan() {
            return GREATER_THAN;
        }

        public static LongBiPredicate greaterEqual() {
            return GREATER_EQUAL;
        }

        public static LongBiPredicate lessThan() {
            return LESS_THAN;
        }

        public static LongBiPredicate lessEqual() {
            return LESS_EQUAL;
        }
    }

    public static final class Doubles {

        private static final DoublePredicate POSITIVE = new DoublePredicate() {
            @Override
            public boolean test(double t) {
                return t > 0;
            }
        };

        private static final DoublePredicate NOT_NEGATIVE = new DoublePredicate() {
            @Override
            public boolean test(double t) {
                return t >= 0;
            }
        };

        private static final DoubleBiPredicate EQUAL = new DoubleBiPredicate() {
            @Override
            public boolean test(double t, double u) {
                return N.equals(t, u);
            }
        };

        private static final DoubleBiPredicate NOT_EQUAL = new DoubleBiPredicate() {
            @Override
            public boolean test(double t, double u) {
                return N.compare(t, u) != 0;
            }
        };

        private static final DoubleBiPredicate GREATER_THAN = new DoubleBiPredicate() {
            @Override
            public boolean test(double t, double u) {
                return N.compare(t, u) > 0;
            }
        };

        private static final DoubleBiPredicate GREATER_EQUAL = new DoubleBiPredicate() {
            @Override
            public boolean test(double t, double u) {
                return N.compare(t, u) >= 0;
            }
        };

        private static final DoubleBiPredicate LESS_THAN = new DoubleBiPredicate() {
            @Override
            public boolean test(double t, double u) {
                return N.compare(t, u) < 0;
            }
        };

        private static final DoubleBiPredicate LESS_EQUAL = new DoubleBiPredicate() {
            @Override
            public boolean test(double t, double u) {
                return N.compare(t, u) <= 0;
            }
        };

        private Doubles() {
            // Utility class.
        }

        public static DoublePredicate positve() {
            return POSITIVE;
        }

        public static DoublePredicate notNegative() {
            return NOT_NEGATIVE;
        }

        public static DoubleBiPredicate equal() {
            return EQUAL;
        }

        public static DoubleBiPredicate notEqual() {
            return NOT_EQUAL;
        }

        public static DoubleBiPredicate greaterThan() {
            return GREATER_THAN;
        }

        public static DoubleBiPredicate greaterEqual() {
            return GREATER_EQUAL;
        }

        public static DoubleBiPredicate lessThan() {
            return LESS_THAN;
        }

        public static DoubleBiPredicate lessEqual() {
            return LESS_EQUAL;
        }
    }

    public static final class Pairs {
        @SuppressWarnings("rawtypes")
        private static final Function PAIR_TO_LIST = new Function() {
            @Override
            public List apply(Pair t) {
                return N.asList(t.getLeft(), t.getRight());
            }

        };

        @SuppressWarnings("rawtypes")
        private static final Function PAIR_TO_SET = new Function() {
            @Override
            public Set apply(Pair t) {
                return N.asSet(t.getLeft(), t.getRight());
            }

        };

        private Pairs() {
            // Utility class.
        }

        @SuppressWarnings("rawtypes")
        public static  Function, List> toList() {
            return (Function) PAIR_TO_LIST;
        }

        @SuppressWarnings("rawtypes")
        public static  Function, Set> toSet() {
            return (Function) PAIR_TO_SET;
        }

    }

    public static final class Triples {

        @SuppressWarnings("rawtypes")
        private static final Function TRIPLE_TO_LIST = new Function() {
            @Override
            public List apply(Triple t) {
                return N.asList(t.getLeft(), t.getMiddle(), t.getRight());
            }

        };

        @SuppressWarnings("rawtypes")
        private static final Function TRIPLE_TO_SET = new Function() {
            @Override
            public Set apply(Triple t) {
                return N.asSet(t.getLeft(), t.getMiddle(), t.getRight());
            }

        };

        private Triples() {
            // Utility class.
        }

        @SuppressWarnings("rawtypes")
        public static  Function, List> toList() {
            return (Function) TRIPLE_TO_LIST;
        }

        @SuppressWarnings("rawtypes")
        public static  Function, Set> toSet() {
            return (Function) TRIPLE_TO_SET;
        }
    }
}
    
    
    
    

    




    
    
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