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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.map.immutable;

import java.io.Serializable;
import java.util.Collection;
import java.util.Map;
import java.util.Set;

import com.gs.collections.api.RichIterable;
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.predicate.Predicate2;
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.map.ImmutableMap;
import com.gs.collections.api.tuple.Pair;
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.utility.LazyIterate;
import net.jcip.annotations.Immutable;

/**
 * This is a zero element {@link ImmutableMap} which is created by calling the Maps.immutable.empty() method.
 */
@Immutable
final class ImmutableEmptyMap
        extends AbstractImmutableMap
        implements Serializable
{
    static final ImmutableMap INSTANCE = new ImmutableEmptyMap();

    private static final long serialVersionUID = 1L;

    public int size()
    {
        return 0;
    }

    public RichIterable keysView()
    {
        return LazyIterate.empty();
    }

    public RichIterable valuesView()
    {
        return LazyIterate.empty();
    }

    public RichIterable> keyValuesView()
    {
        return LazyIterate.empty();
    }

    public boolean containsKey(Object key)
    {
        return false;
    }

    public boolean containsValue(Object value)
    {
        return false;
    }

    public V get(Object key)
    {
        return null;
    }

    public Set keySet()
    {
        return Sets.immutable.of().castToSet();
    }

    public Collection values()
    {
        return Lists.immutable.empty().castToList();
    }

    @Override
    public String toString()
    {
        return "{}";
    }

    @Override
    public boolean equals(Object other)
    {
        if (!(other instanceof Map))
        {
            return false;
        }

        return ((Map) other).isEmpty();
    }

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

    public void forEachKeyValue(Procedure2 procedure)
    {
    }

    @Override
    public ImmutableMap flipUniqueValues()
    {
        return Maps.immutable.with();
    }

    @Override
    public void forEachKey(Procedure procedure)
    {
    }

    @Override
    public void forEachValue(Procedure procedure)
    {
    }

    @Override
    public void forEachWithIndex(ObjectIntProcedure objectIntProcedure)
    {
    }

    @Override
    public  void forEachWith(Procedure2 procedure, P parameter)
    {
    }

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

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

    @Override
    public void each(Procedure procedure)
    {
    }

    @Override
    public  A ifPresentApply(K key, Function function)
    {
        return null;
    }

    @Override
    public V getIfAbsent(K key, Function0 function)
    {
        return function.value();
    }

    @Override
    public V getIfAbsentValue(K key, V value)
    {
        return value;
    }

    @Override
    public  V getIfAbsentWith(
            K key,
            Function function,
            P parameter)
    {
        return function.valueOf(parameter);
    }

    @Override
    public  ImmutableMap collect(Function2> function)
    {
        return Maps.immutable.empty();
    }

    @Override
    public  ImmutableMap collectValues(Function2 function)
    {
        return Maps.immutable.empty();
    }

    @Override
    public Pair detect(Predicate2 predicate)
    {
        return null;
    }

    @Override
    public ImmutableMap reject(Predicate2 predicate)
    {
        return this;
    }

    @Override
    public ImmutableMap select(Predicate2 predicate)
    {
        return this;
    }

    private Object writeReplace()
    {
        return new ImmutableMapSerializationProxy(this);
    }
}