WeakHashSet.java

// Copyright 2008 Google Inc.
//
// 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.google.android.stardroid.util;

import java.util.AbstractSet;
import java.util.Iterator;
import java.util.Set;
import java.util.WeakHashMap;

/**
 * This is to WeakHashMap as HashSet is to HashMap.  Basically, entries are held
 * with weak references and can be gc'd when other clients have finished with
 * them.
 */
public class WeakHashSet<E> extends AbstractSet<E> implements Set<E> {
  private final WeakHashMap<E, Void> hashMap = new WeakHashMap<E, Void>();

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

  @Override
  public boolean add(E object) {
    if (hashMap.containsKey(object)) {
      return false;
    }
    hashMap.put(object, null);
    return true;
  }

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