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GS Collections is a collections framework for Java. It has JDK-compatible List, Set and Map implementations with a rich API and set of utility classes that work with any JDK compatible Collections, Arrays, Maps or Strings. The iteration protocol was inspired by the Smalltalk collection framework.

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/*
 * Copyright 2015 Goldman Sachs.
 *
 * 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.gs.collections.impl.bag.immutable;

import java.io.IOException;
import java.io.Serializable;
import java.util.Comparator;
import java.util.Iterator;
import java.util.NoSuchElementException;

import com.gs.collections.api.LazyIterable;
import com.gs.collections.api.RichIterable;
import com.gs.collections.api.bag.Bag;
import com.gs.collections.api.bag.ImmutableBag;
import com.gs.collections.api.bag.MutableBag;
import com.gs.collections.api.bag.primitive.ImmutableBooleanBag;
import com.gs.collections.api.bag.primitive.ImmutableByteBag;
import com.gs.collections.api.bag.primitive.ImmutableCharBag;
import com.gs.collections.api.bag.primitive.ImmutableDoubleBag;
import com.gs.collections.api.bag.primitive.ImmutableFloatBag;
import com.gs.collections.api.bag.primitive.ImmutableIntBag;
import com.gs.collections.api.bag.primitive.ImmutableLongBag;
import com.gs.collections.api.bag.primitive.ImmutableShortBag;
import com.gs.collections.api.bag.sorted.MutableSortedBag;
import com.gs.collections.api.block.function.Function;
import com.gs.collections.api.block.function.Function0;
import com.gs.collections.api.block.function.Function2;
import com.gs.collections.api.block.function.primitive.BooleanFunction;
import com.gs.collections.api.block.function.primitive.ByteFunction;
import com.gs.collections.api.block.function.primitive.CharFunction;
import com.gs.collections.api.block.function.primitive.DoubleFunction;
import com.gs.collections.api.block.function.primitive.FloatFunction;
import com.gs.collections.api.block.function.primitive.IntFunction;
import com.gs.collections.api.block.function.primitive.LongFunction;
import com.gs.collections.api.block.function.primitive.ShortFunction;
import com.gs.collections.api.block.predicate.Predicate;
import com.gs.collections.api.block.predicate.Predicate2;
import com.gs.collections.api.block.predicate.primitive.IntPredicate;
import com.gs.collections.api.block.procedure.Procedure;
import com.gs.collections.api.block.procedure.Procedure2;
import com.gs.collections.api.block.procedure.primitive.ObjectIntProcedure;
import com.gs.collections.api.list.MutableList;
import com.gs.collections.api.map.ImmutableMap;
import com.gs.collections.api.map.MutableMap;
import com.gs.collections.api.map.sorted.MutableSortedMap;
import com.gs.collections.api.multimap.bag.ImmutableBagMultimap;
import com.gs.collections.api.ordered.OrderedIterable;
import com.gs.collections.api.partition.bag.PartitionImmutableBag;
import com.gs.collections.api.set.ImmutableSet;
import com.gs.collections.api.set.MutableSet;
import com.gs.collections.api.tuple.Pair;
import com.gs.collections.impl.EmptyIterator;
import com.gs.collections.impl.bag.mutable.HashBag;
import com.gs.collections.impl.bag.sorted.mutable.TreeBag;
import com.gs.collections.impl.block.factory.Comparators;
import com.gs.collections.impl.factory.Bags;
import com.gs.collections.impl.factory.Lists;
import com.gs.collections.impl.factory.Maps;
import com.gs.collections.impl.factory.Sets;
import com.gs.collections.impl.factory.primitive.BooleanBags;
import com.gs.collections.impl.factory.primitive.ByteBags;
import com.gs.collections.impl.factory.primitive.CharBags;
import com.gs.collections.impl.factory.primitive.DoubleBags;
import com.gs.collections.impl.factory.primitive.FloatBags;
import com.gs.collections.impl.factory.primitive.IntBags;
import com.gs.collections.impl.factory.primitive.LongBags;
import com.gs.collections.impl.factory.primitive.ShortBags;
import com.gs.collections.impl.map.mutable.UnifiedMap;
import com.gs.collections.impl.map.sorted.mutable.TreeSortedMap;
import com.gs.collections.impl.multimap.bag.HashBagMultimap;
import com.gs.collections.impl.partition.bag.PartitionHashBag;
import com.gs.collections.impl.utility.ArrayIterate;
import com.gs.collections.impl.utility.Iterate;
import com.gs.collections.impl.utility.LazyIterate;
import net.jcip.annotations.Immutable;

/**
 * This is a zero element {@link ImmutableBag} which is created by calling the Bags.immutable.empty().
 *
 * @since 1.0
 */
@Immutable
final class ImmutableEmptyBag
        extends AbstractImmutableBag
        implements Serializable
{
    static final ImmutableBag INSTANCE = new ImmutableEmptyBag();

    private static final long serialVersionUID = 1L;

    private static final LazyIterable LAZY_ITERABLE = LazyIterate.adapt(INSTANCE);
    private static final Object[] TO_ARRAY = new Object[0];
    private static final PartitionImmutableBag IMMUTABLE_EMPTY_PARTITION = new PartitionHashBag().toImmutable();

    @Override
    public boolean equals(Object obj)
    {
        if (obj == this)
        {
            return true;
        }
        return obj instanceof Bag && ((Bag) obj).isEmpty();
    }

    public int sizeDistinct()
    {
        return 0;
    }

    public int occurrencesOf(Object item)
    {
        return 0;
    }

    public void forEachWithOccurrences(ObjectIntProcedure objectIntProcedure)
    {
    }

    public MutableMap toMapOfItemToCount()
    {
        return Maps.mutable.empty();
    }

    @Override
    public int hashCode()
    {
        return 0;
    }

    public int size()
    {
        return 0;
    }

    @Override
    public boolean isEmpty()
    {
        return true;
    }

    @Override
    public boolean notEmpty()
    {
        return false;
    }

    @Override
    public boolean contains(Object object)
    {
        return false;
    }

    @Override
    public boolean containsAllIterable(Iterable source)
    {
        return Iterate.isEmpty(source);
    }

    @Override
    public boolean containsAllArguments(Object... elements)
    {
        return ArrayIterate.isEmpty(elements);
    }

    @Override
    public ImmutableBag tap(Procedure procedure)
    {
        return this;
    }

    public void each(Procedure procedure)
    {
    }

    @Override
    public void forEachWithIndex(ObjectIntProcedure objectIntProcedure)
    {
    }

    @Override
    public 

void forEachWith(Procedure2 procedure, P parameter) { } public T getFirst() { return null; } public T getLast() { return null; } public Iterator iterator() { return EmptyIterator.getInstance(); } public ImmutableBag newWith(T element) { return Bags.immutable.with(element); } public ImmutableBag newWithout(T element) { return this; } public ImmutableBag newWithAll(Iterable elements) { return HashBag.newBag(elements).toImmutable(); } public ImmutableBag selectByOccurrences(IntPredicate predicate) { return this; } public ImmutableBag select(Predicate predicate) { return this; } @Override public

ImmutableBag selectWith(Predicate2 predicate, P parameter) { return this; } public ImmutableBag reject(Predicate predicate) { return this; } @Override public

ImmutableBag rejectWith(Predicate2 predicate, P parameter) { return this; } @Override public PartitionImmutableBag partition(Predicate predicate) { return (PartitionImmutableBag) IMMUTABLE_EMPTY_PARTITION; } @Override public

PartitionImmutableBag partitionWith(Predicate2 predicate, P parameter) { return (PartitionImmutableBag) IMMUTABLE_EMPTY_PARTITION; } public ImmutableBag selectInstancesOf(Class clazz) { return (ImmutableBag) INSTANCE; } public ImmutableBag collect(Function function) { return (ImmutableBag) INSTANCE; } @Override public ImmutableBooleanBag collectBoolean(BooleanFunction booleanFunction) { return BooleanBags.immutable.empty(); } @Override public ImmutableByteBag collectByte(ByteFunction byteFunction) { return ByteBags.immutable.empty(); } @Override public ImmutableCharBag collectChar(CharFunction charFunction) { return CharBags.immutable.empty(); } @Override public ImmutableDoubleBag collectDouble(DoubleFunction doubleFunction) { return DoubleBags.immutable.empty(); } @Override public ImmutableFloatBag collectFloat(FloatFunction floatFunction) { return FloatBags.immutable.empty(); } @Override public ImmutableIntBag collectInt(IntFunction intFunction) { return IntBags.immutable.empty(); } @Override public ImmutableLongBag collectLong(LongFunction longFunction) { return LongBags.immutable.empty(); } @Override public ImmutableShortBag collectShort(ShortFunction shortFunction) { return ShortBags.immutable.empty(); } @Override public ImmutableBag collectWith(Function2 function, P parameter) { return (ImmutableBag) INSTANCE; } public ImmutableBag collectIf( Predicate predicate, Function function) { return (ImmutableBag) INSTANCE; } public ImmutableBag flatCollect(Function> function) { return (ImmutableBag) INSTANCE; } public ImmutableBagMultimap groupBy(Function function) { // TODO: Create a Singleton ImmutableEmptyBagMultimap for efficiency return HashBagMultimap.newMultimap().toImmutable(); } public ImmutableBagMultimap groupByEach(Function> function) { // TODO: Create a Singleton ImmutableEmptyBagMultimap for efficiency return HashBagMultimap.newMultimap().toImmutable(); } @Override public ImmutableMap groupByUniqueKey(Function function) { return Maps.immutable.empty(); } @Override public T detect(Predicate predicate) { return null; } @Override public

T detectWith(Predicate2 predicate, P parameter) { return null; } @Override public T detectIfNone(Predicate predicate, Function0 function) { return function.value(); } @Override public

T detectWithIfNone(Predicate2 predicate, P parameter, Function0 function) { return function.value(); } @Override public int count(Predicate predicate) { return 0; } @Override public

int countWith(Predicate2 predicate, P parameter) { return 0; } @Override public boolean anySatisfy(Predicate predicate) { return false; } @Override public boolean allSatisfy(Predicate predicate) { return true; } @Override public boolean noneSatisfy(Predicate predicate) { return true; } @Override public

boolean anySatisfyWith(Predicate2 predicate, P parameter) { return false; } @Override public

boolean allSatisfyWith(Predicate2 predicate, P parameter) { return true; } @Override public

boolean noneSatisfyWith(Predicate2 predicate, P parameter) { return true; } @Override public IV injectInto(IV injectedValue, Function2 function) { return injectedValue; } @Override public MutableList toList() { return Lists.mutable.empty(); } @Override public MutableList toSortedList() { return Lists.mutable.empty(); } @Override public MutableList toSortedList(Comparator comparator) { return Lists.mutable.empty(); } @Override public > MutableList toSortedListBy(Function function) { return Lists.mutable.empty(); } @Override public MutableSet toSet() { return Sets.mutable.empty(); } @Override public MutableBag toBag() { return Bags.mutable.empty(); } @Override public MutableSortedBag toSortedBag() { return TreeBag.newBag(); } @Override public MutableSortedBag toSortedBag(Comparator comparator) { return TreeBag.newBag(comparator); } @Override public > MutableSortedBag toSortedBagBy(Function function) { return TreeBag.newBag(Comparators.byFunction(function)); } @Override public MutableMap toMap( Function keyFunction, Function valueFunction) { return UnifiedMap.newMap(); } @Override public MutableSortedMap toSortedMap( Function keyFunction, Function valueFunction) { return TreeSortedMap.newMap(); } @Override public MutableSortedMap toSortedMap(Comparator comparator, Function keyFunction, Function valueFunction) { return TreeSortedMap.newMap(comparator); } @Override public LazyIterable asLazy() { return (LazyIterable) LAZY_ITERABLE; } @Override public Object[] toArray() { return TO_ARRAY; } @Override public T[] toArray(T[] a) { if (a.length > 0) { a[0] = null; } return a; } @Override public T min(Comparator comparator) { throw new NoSuchElementException(); } @Override public T max(Comparator comparator) { throw new NoSuchElementException(); } @Override public T min() { throw new NoSuchElementException(); } @Override public T max() { throw new NoSuchElementException(); } @Override public > T minBy(Function function) { throw new NoSuchElementException(); } @Override public > T maxBy(Function function) { throw new NoSuchElementException(); } @Override public String toString() { return "[]"; } @Override public String makeString() { return ""; } @Override public String makeString(String separator) { return ""; } @Override public String makeString(String start, String separator, String end) { return start + end; } @Override public void appendString(Appendable appendable) { } @Override public void appendString(Appendable appendable, String separator) { } @Override public void appendString(Appendable appendable, String start, String separator, String end) { try { appendable.append(start); appendable.append(end); } catch (IOException e) { throw new RuntimeException(e); } } /** * @deprecated in 6.0. Use {@link OrderedIterable#zip(Iterable)} instead. */ @Deprecated public ImmutableBag> zip(Iterable that) { return Bags.immutable.empty(); } /** * @deprecated in 6.0. Use {@link OrderedIterable#zipWithIndex()} instead. */ @Deprecated public ImmutableSet> zipWithIndex() { return Sets.immutable.empty(); } @Override public RichIterable> chunk(int size) { if (size <= 0) { throw new IllegalArgumentException("Size for groups must be positive but was: " + size); } return Bags.immutable.empty(); } private Object writeReplace() { return new ImmutableBagSerializationProxy(this); } }