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feilong is a suite of core and expanded libraries that include utility classes, http, excel,cvs, io classes, and much much more.
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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.feilong.lib.collection4;

import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;
import java.util.Map;
import java.util.Set;

import org.apache.commons.collections4.Equator;
import org.apache.commons.collections4.Predicate;
import org.apache.commons.collections4.Transformer;

/**
 * Provides utility methods and decorators for {@link Collection} instances.
 * 
 * Various utility methods might put the input objects into a Set/Map/Bag. In case
 * the input objects override {@link Object#equals(Object)}, it is mandatory that
 * the general contract of the {@link Object#hashCode()} method is maintained.
 * 
 * 
 * NOTE: From 4.0, method parameters will take {@link Iterable} objects when possible.
 * 
 *
 * @since 1.0
 */
public class CollectionUtils{

    /**
     * Helper class to easily access cardinality properties of two collections.
     * 
     * @param 
     *            the element type
     */
    private static class CardinalityHelper {

        /** Contains the cardinality for each object in collection A. */
        final Map cardinalityA;

        /** Contains the cardinality for each object in collection B. */
        final Map cardinalityB;

        /**
         * Create a new CardinalityHelper for two collections.
         * 
         * @param a
         *            the first collection
         * @param b
         *            the second collection
         */
        public CardinalityHelper(final Iterable a, final Iterable b){
            cardinalityA = CollectionUtils. getCardinalityMap(a);
            cardinalityB = CollectionUtils. getCardinalityMap(b);
        }

        /**
         * Returns the maximum frequency of an object.
         * 
         * @param obj
         *            the object
         * @return the maximum frequency of the object
         */
        public final int max(final Object obj){
            return Math.max(freqA(obj), freqB(obj));
        }

        /**
         * Returns the minimum frequency of an object.
         * 
         * @param obj
         *            the object
         * @return the minimum frequency of the object
         */
        public final int min(final Object obj){
            return Math.min(freqA(obj), freqB(obj));
        }

        /**
         * Returns the frequency of this object in collection A.
         * 
         * @param obj
         *            the object
         * @return the frequency of the object in collection A
         */
        public int freqA(final Object obj){
            return getFreq(obj, cardinalityA);
        }

        /**
         * Returns the frequency of this object in collection B.
         * 
         * @param obj
         *            the object
         * @return the frequency of the object in collection B
         */
        public int freqB(final Object obj){
            return getFreq(obj, cardinalityB);
        }

        private static int getFreq(final Object obj,final Map freqMap){
            final Integer count = freqMap.get(obj);
            if (count != null){
                return count.intValue();
            }
            return 0;
        }
    }

    /**
     * Helper class for set-related operations, e.g. union, subtract, intersection.
     * 
     * @param 
     *            the element type
     */
    private static class SetOperationCardinalityHelper extends CardinalityHelper implements Iterable{

        /** Contains the unique elements of the two collections. */
        private final Set  elements;

        /** Output collection. */
        private final List newList;

        /**
         * Create a new set operation helper from the two collections.
         * 
         * @param a
         *            the first collection
         * @param b
         *            the second collection
         */
        public SetOperationCardinalityHelper(final Iterable a, final Iterable b){
            super(a, b);
            elements = new HashSet<>();
            addAll(elements, a);
            addAll(elements, b);
            // the resulting list must contain at least each unique element, but may grow
            newList = new ArrayList<>(elements.size());
        }

        @Override
        public Iterator iterator(){
            return elements.iterator();
        }

        /**
         * Add the object {@code count} times to the result collection.
         * 
         * @param obj
         *            the object to add
         * @param count
         *            the count
         */
        public void setCardinality(final O obj,final int count){
            for (int i = 0; i < count; i++){
                newList.add(obj);
            }
        }

        /**
         * Returns the resulting collection.
         * 
         * @return the result
         */
        public Collection list(){
            return newList;
        }

    }

    /**
     * An empty unmodifiable collection.
     * The JDK provides empty Set and List implementations which could be used for
     * this purpose. However they could be cast to Set or List which might be
     * undesirable. This implementation only implements Collection.
     */
    @SuppressWarnings("rawtypes") // we deliberately use the raw type here
    public static final Collection EMPTY_COLLECTION = Collections.emptyList();

    /**
     * CollectionUtils should not normally be instantiated.
     */
    private CollectionUtils(){
    }

    /**
     * Returns the immutable EMPTY_COLLECTION with generic type safety.
     *
     * @see #EMPTY_COLLECTION
     * @since 4.0
     * @param 
     *            the element type
     * @return immutable empty collection
     */
    @SuppressWarnings("unchecked") // OK, empty collection is compatible with any type
    public static  Collection emptyCollection(){
        return EMPTY_COLLECTION;
    }

    /**
     * Returns an immutable empty collection if the argument is null,
     * or the argument itself otherwise.
     *
     * @param 
     *            the element type
     * @param collection
     *            the collection, possibly null
     * @return an empty collection if the argument is null
     */
    public static  Collection emptyIfNull(final Collection collection){
        return collection == null ? CollectionUtils. emptyCollection() : collection;
    }

    /**
     * Returns a {@link Collection} containing the union of the given
     * {@link Iterable}s.
     * 
     * The cardinality of each element in the returned {@link Collection} will
     * be equal to the maximum of the cardinality of that element in the two
     * given {@link Iterable}s.
     * 
     *
     * @param a
     *            the first collection, must not be null
     * @param b
     *            the second collection, must not be null
     * @param 
     *            the generic type that is able to represent the types contained
     *            in both input collections.
     * @return the union of the two collections
     * @see Collection#addAll
     */
    public static  Collection union(final Iterable a,final Iterable b){
        final SetOperationCardinalityHelper helper = new SetOperationCardinalityHelper<>(a, b);
        for (final O obj : helper){
            helper.setCardinality(obj, helper.max(obj));
        }
        return helper.list();
    }

    /**
     * Returns a {@link Collection} containing the intersection of the given
     * {@link Iterable}s.
     * 
     * The cardinality of each element in the returned {@link Collection} will
     * be equal to the minimum of the cardinality of that element in the two
     * given {@link Iterable}s.
     * 
     *
     * @param a
     *            the first collection, must not be null
     * @param b
     *            the second collection, must not be null
     * @param 
     *            the generic type that is able to represent the types contained
     *            in both input collections.
     * @return the intersection of the two collections
     * @see Collection#retainAll
     */
    public static  Collection intersection(final Iterable a,final Iterable b){
        final SetOperationCardinalityHelper helper = new SetOperationCardinalityHelper<>(a, b);
        for (final O obj : helper){
            helper.setCardinality(obj, helper.min(obj));
        }
        return helper.list();
    }

    /**
     * Returns a {@link Collection} containing the exclusive disjunction
     * (symmetric difference) of the given {@link Iterable}s.
     * 
     * The cardinality of each element e in the returned
     * {@link Collection} will be equal to
     * max(cardinality(e,a),cardinality(e,b)) - min(cardinality(e,a),
     * cardinality(e,b)).
     * 
     * 
     * This is equivalent to
     * {@code {@link #subtract subtract}({@link #union union(a,b)},{@link #intersection intersection(a,b)})}
     * or
     * {@code {@link #union union}({@link #subtract subtract(a,b)},{@link #subtract subtract(b,a)})}.
     * 
     *
     * @param a
     *            the first collection, must not be null
     * @param b
     *            the second collection, must not be null
     * @param 
     *            the generic type that is able to represent the types contained
     *            in both input collections.
     * @return the symmetric difference of the two collections
     */
    public static  Collection disjunction(final Iterable a,final Iterable b){
        final SetOperationCardinalityHelper helper = new SetOperationCardinalityHelper<>(a, b);
        for (final O obj : helper){
            helper.setCardinality(obj, helper.max(obj) - helper.min(obj));
        }
        return helper.list();
    }

    /**
     * Returns true iff all elements of {@code coll2} are also contained
     * in {@code coll1}. The cardinality of values in {@code coll2} is not taken into account,
     * which is the same behavior as {@link Collection#containsAll(Collection)}.
     * 
     * In other words, this method returns true iff the
     * {@link #intersection} of coll1 and coll2 has the same cardinality as
     * the set of unique values from {@code coll2}. In case {@code coll2} is empty, {@code true}
     * will be returned.
     * 
     * 
     * This method is intended as a replacement for {@link Collection#containsAll(Collection)}
     * with a guaranteed runtime complexity of {@code O(n + m)}. Depending on the type of
     * {@link Collection} provided, this method will be much faster than calling
     * {@link Collection#containsAll(Collection)} instead, though this will come at the
     * cost of an additional space complexity O(n).
     * 
     *
     * @param coll1
     *            the first collection, must not be null
     * @param coll2
     *            the second collection, must not be null
     * @return true iff the intersection of the collections has the same cardinality
     *         as the set of unique elements from the second collection
     * @since 4.0
     */
    public static boolean containsAll(final Collection coll1,final Collection coll2){
        if (coll2.isEmpty()){
            return true;
        }
        final Iterator it = coll1.iterator();
        final Set