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OpenJPA Utilities Library
There is a newer version: 4.0.1
/*
 * 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.openjpa.lib.util;

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

import org.apache.commons.collections.set.MapBackedSet;

/**
 * A set whose values may be stored as weak or soft references.
 *
 * @author Abe White
 */
public class ReferenceHashSet implements Set, Serializable {

    /**
     * Hard reference marker.
     */
    public static final int HARD = 0;

    /**
     * Soft reference marker.
     */
    public static final int SOFT = 1;

    /**
     * Weak reference marker.
     */
    public static final int WEAK = 2;

    private static final Object DUMMY_VAL = new Serializable() {
        public String toString() {
            return ReferenceHashSet.class.getName() + ".DUMMY_VAL";
        }
    };

    private final Set _set;

    /**
     * Construct a set with the given reference type.
     */
    public ReferenceHashSet(int refType) {
        if (refType == HARD)
            _set = new HashSet();
        else {
            int mapRefType = (refType == WEAK) ? org.apache.commons.
                collections.map.ReferenceMap.WEAK : org.apache.
                commons.collections.map.ReferenceMap.SOFT;
            _set = MapBackedSet.decorate(new org.apache.commons.
                collections.map.ReferenceMap(mapRefType,
                org.apache.commons.collections.map.
                    ReferenceMap.HARD), DUMMY_VAL);
        }
    }

    public boolean add(Object obj) {
        return _set.add(obj);
    }

    public boolean addAll(Collection coll) {
        return _set.addAll(coll);
    }

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

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

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

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

    public Iterator iterator() {
        return _set.iterator();
    }

    public boolean remove(Object obj) {
        return _set.remove(obj);
    }

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

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

    public int size() {
        return _set.size();
    }

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

    public Object[] toArray(Object[] arr) {
        return _set.toArray(arr);
    }

    public int hashCode() {
        return _set.hashCode();
    }

    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj instanceof ReferenceHashSet)
            obj = ((ReferenceHashSet) obj)._set;
        return _set.equals(obj);
    }
}