MapBackedSet.java example

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/*
 * Copyright 2011 The Netty Project
 *
 * The Netty Project 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.jboss.netty.util;

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

/**
 * A {@link Map}-backed {@link Set}.
 */
final class MapBackedSet<E> extends AbstractSet<E> implements Serializable {

    private static final long serialVersionUID = -6761513279741915432L;

    private final Map<E, Boolean> map;

    /**
     * Creates a new instance which wraps the specified {@code map}.
     */
    MapBackedSet(Map<E, Boolean> map) {
        this.map = map;
    }

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

    @Override
    public boolean contains(Object o) {
        return map.containsKey(o);
    }

    @Override
    public boolean add(E o) {
        return map.put(o, Boolean.TRUE) == null;
    }

    @Override
    public boolean remove(Object o) {
        return map.remove(o) != null;
    }

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

    @Override
    public Iterator<E> iterator() {
        return map.keySet().iterator();
    }
}