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Commons Collections example source code file (MapBackedSet.java)

This example Commons Collections source code file (MapBackedSet.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Commons Collections tags/keywords

illegalargumentexception, io, iterator, iterator, map, mapbackedset, mapbackedset, object, object, serializable, set, set, the, util

The Commons Collections MapBackedSet.java source code

/*
 *  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.collections.set;

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

/**
 * Decorates a <code>Map to obtain Set behaviour.
 * <p>
 * This class is used to create a <code>Set with the same properties as
 * the key set of any map. Thus, a ReferenceSet can be created by wrapping a
 * <code>ReferenceMap in an instance of this class.
 * <p>
 * Most map implementation can be used to create a set by passing in dummy values.
 * Exceptions include <code>BidiMap implementations, as they require unique values.
 *
 * @since Commons Collections 3.1
 * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
 * 
 * @author Stephen Colebourne
 */
public final class MapBackedSet implements Set, Serializable {

    /** Serialization version */
    private static final long serialVersionUID = 6723912213766056587L;

    /** The map being used as the backing store */
    protected final Map map;
    /** The dummyValue to use */
    protected final Object dummyValue;

    /**
     * Factory method to create a set from a map.
     * 
     * @param map  the map to decorate, must not be null
     * @throws IllegalArgumentException if set is null
     */
    public static Set decorate(Map map) {
        return decorate(map, null);
    }

    /**
     * Factory method to create a set from a map.
     * 
     * @param map  the map to decorate, must not be null
     * @param dummyValue  the dummy value to use
     * @throws IllegalArgumentException if map is null
     */
    public static Set decorate(Map map, Object dummyValue) {
        if (map == null) {
            throw new IllegalArgumentException("The map must not be null");
        }
        return new MapBackedSet(map, dummyValue);
    }

    //-----------------------------------------------------------------------
    /**
     * Constructor that wraps (not copies).
     * 
     * @param map  the map to decorate, must not be null
     * @param dummyValue  the dummy value to use
     * @throws IllegalArgumentException if map is null
     */
    private MapBackedSet(Map map, Object dummyValue) {
        super();
        this.map = map;
        this.dummyValue = dummyValue;
    }

    //-----------------------------------------------------------------------
    public int size() {
        return map.size();
    }

    public boolean isEmpty() {
        return map.isEmpty();
    }

    public Iterator iterator() {
        return map.keySet().iterator();
    }

    public boolean contains(Object obj) {
        return map.containsKey(obj);
    }

    public boolean containsAll(Collection coll) {
        return map.keySet().containsAll(coll);
    }

    public boolean add(Object obj) {
        int size = map.size();
        map.put(obj, dummyValue);
        return (map.size() != size);
    }

    public boolean addAll(Collection coll) {
        int size = map.size();
        for (Iterator it = coll.iterator(); it.hasNext();) {
            Object obj = it.next();
            map.put(obj, dummyValue);
        }
        return (map.size() != size);
    }

    public boolean remove(Object obj) {
        int size = map.size();
        map.remove(obj);
        return (map.size() != size);
    }

    public boolean removeAll(Collection coll) {
        return map.keySet().removeAll(coll);
    }

    public boolean retainAll(Collection coll) {
        return map.keySet().retainAll(coll);
    }

    public void clear() {
        map.clear();
    }

    public Object[] toArray() {
        return map.keySet().toArray();
    }

    public Object[] toArray(Object[] array) {
        return map.keySet().toArray(array);
    }

    public boolean equals(Object obj) {
        return map.keySet().equals(obj);
    }

    public int hashCode() {
        return map.keySet().hashCode();
    }

}

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