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The Apache Commons Collections package contains types that extend and augment the Java Collections Framework.
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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 org.apache.commons.collections4.map;

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

/**
 * Provides a base decorator that enables additional functionality to be added
 * to a Map via decoration.
 * 
 * Methods are forwarded directly to the decorated map.
 * 
 * 
 * This implementation does not perform any special processing with
 * {@link #entrySet()}, {@link #keySet()} or {@link #values()}. Instead
 * it simply returns the set/collection from the wrapped map. This may be
 * undesirable, for example if you are trying to write a validating
 * implementation it would provide a loophole around the validation.
 * But, you might want that loophole, so this class is kept simple.
 * 
 *
 * @param  the type of the keys in the map
 * @param  the type of the values in the map
 * @since 3.0
 */
public abstract class AbstractMapDecorator extends AbstractIterableMap {

    /** The map to decorate */
    transient Map map;

    /**
     * Constructor only used in deserialization, do not use otherwise.
     * @since 3.1
     */
    protected AbstractMapDecorator() {
        super();
    }

    /**
     * Constructor that wraps (not copies).
     *
     * @param map  the map to decorate, must not be null
     * @throws NullPointerException if the map is null
     */
    protected AbstractMapDecorator(final Map map) {
        if (map == null) {
            throw new NullPointerException("Map must not be null.");
        }
        this.map = map;
    }

    /**
     * Gets the map being decorated.
     *
     * @return the decorated map
     */
    protected Map decorated() {
        return map;
    }

    //-----------------------------------------------------------------------
    @Override
    public void clear() {
        decorated().clear();
    }

    @Override
    public boolean containsKey(final Object key) {
        return decorated().containsKey(key);
    }

    @Override
    public boolean containsValue(final Object value) {
        return decorated().containsValue(value);
    }

    @Override
    public Set> entrySet() {
        return decorated().entrySet();
    }

    @Override
    public V get(final Object key) {
        return decorated().get(key);
    }

    @Override
    public boolean isEmpty() {
        return decorated().isEmpty();
    }

    @Override
    public Set keySet() {
        return decorated().keySet();
    }

    @Override
    public V put(final K key, final V value) {
        return decorated().put(key, value);
    }

    @Override
    public void putAll(final Map mapToCopy) {
        decorated().putAll(mapToCopy);
    }

    @Override
    public V remove(final Object key) {
        return decorated().remove(key);
    }

    @Override
    public int size() {
        return decorated().size();
    }

    @Override
    public Collection values() {
        return decorated().values();
    }

    @Override
    public boolean equals(final Object object) {
        if (object == this) {
            return true;
        }
        return decorated().equals(object);
    }

    @Override
    public int hashCode() {
        return decorated().hashCode();
    }

    @Override
    public String toString() {
        return decorated().toString();
    }

}