001/*
002 * Copyright (C) 2007 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
005 * in compliance with the License. You may obtain a copy of the License at
006 *
007 * http://www.apache.org/licenses/LICENSE-2.0
008 *
009 * Unless required by applicable law or agreed to in writing, software distributed under the License
010 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
011 * or implied. See the License for the specific language governing permissions and limitations under
012 * the License.
013 */
014
015package com.google.common.base;
016
017import com.google.common.annotations.GwtIncompatible;
018import com.google.common.annotations.J2ktIncompatible;
019import java.lang.ref.ReferenceQueue;
020import java.lang.ref.WeakReference;
021import javax.annotation.CheckForNull;
022
023/**
024 * Weak reference with a {@code finalizeReferent()} method which a background thread invokes after
025 * the garbage collector reclaims the referent. This is a simpler alternative to using a {@link
026 * ReferenceQueue}.
027 *
028 * @author Bob Lee
029 * @since 2.0
030 */
031@J2ktIncompatible
032@GwtIncompatible
033@ElementTypesAreNonnullByDefault
034public abstract class FinalizableWeakReference<T> extends WeakReference<T>
035    implements FinalizableReference {
036  /**
037   * Constructs a new finalizable weak reference.
038   *
039   * @param referent to weakly reference
040   * @param queue that should finalize the referent
041   */
042  protected FinalizableWeakReference(@CheckForNull T referent, FinalizableReferenceQueue queue) {
043    super(referent, queue.queue);
044    queue.cleanUp();
045  }
046}