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Java example source code file (WeakKeySet.java)

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

Learn more about this Java project at its project page.

Java - Java tags/keywords

cache, class, keyandsource, map, multiset, object, override, removallistener, set, state, util, weakkeyset

The WeakKeySet.java Java example source code

 * Copyright (C) 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,
 * See the License for the specific language governing permissions and
 * limitations under the License.

package com.google.inject.internal;

import com.google.common.base.Objects;
import com.google.common.base.Preconditions;
import com.google.common.cache.Cache;
import com.google.common.cache.CacheBuilder;
import com.google.common.cache.RemovalCause;
import com.google.common.cache.RemovalListener;
import com.google.common.cache.RemovalNotification;
import com.google.common.collect.LinkedHashMultiset;
import com.google.common.collect.Maps;
import com.google.common.collect.Multiset;
import com.google.common.collect.Sets;
import com.google.inject.Key;
import com.google.inject.internal.util.SourceProvider;

import java.util.Map;
import java.util.Set;

 * Minimal set that doesn't hold strong references to the contained keys.
 * @author dweis@google.com (Daniel Weis)
final class WeakKeySet {

  private Map<Key> backingMap;

   * This is already locked externally on add and getSources but we need it to handle clean up in
   * the evictionCache's RemovalListener.
  private final Object lock;

   * Tracks child injector lifetimes and evicts blacklisted keys/sources after the child injector is
   * garbage collected.
  private final Cache<State, Set evictionCache = CacheBuilder.newBuilder()
          new RemovalListener<State, Set() {
            public void onRemoval(RemovalNotification<State, Set notification) {


   * There may be multiple child injectors blacklisting a certain key so only remove the source
   * that's relevant.
  private void cleanUpForCollectedState(Set<KeyAndSource> keysAndSources) {
    synchronized (lock) {
      for (KeyAndSource keyAndSource : keysAndSources) {
        Multiset<Object> set = backingMap.get(keyAndSource.key);
        if (set != null) {
          if (set.isEmpty()) {

  WeakKeySet(Object lock) {
    this.lock = lock;

  public void add(Key<?> key, State state, Object source) {
    if (backingMap == null) {
      backingMap = Maps.newHashMap();
    // if it's an instanceof Class, it was a JIT binding, which we don't
    // want to retain.
    if (source instanceof Class || source == SourceProvider.UNKNOWN_SOURCE) {
      source = null;
    Multiset<Object> sources = backingMap.get(key);
    if (sources == null) {
      sources = LinkedHashMultiset.create();
      backingMap.put(key, sources);
    Object convertedSource = Errors.convert(source);

    // Avoid all the extra work if we can.
    if (state.parent() != State.NONE) {
      Set<KeyAndSource> keyAndSources = evictionCache.getIfPresent(state);
      if (keyAndSources == null) {
        evictionCache.put(state, keyAndSources = Sets.newHashSet());
      keyAndSources.add(new KeyAndSource(key, convertedSource));

  public boolean contains(Key<?> key) {
    return backingMap != null && backingMap.containsKey(key);

  public Set<Object> getSources(Key key) {
    Multiset<Object> sources = (backingMap == null) ? null : backingMap.get(key);
    return (sources == null) ? null : sources.elementSet();

  private static final class KeyAndSource {
    final Key<?> key;
    final Object source;

    KeyAndSource(Key<?> key, Object source) {
      this.key = key;
      this.source = source;

    public int hashCode() {
      return Objects.hashCode(key, source);

    public boolean equals(Object obj) {
      if (this == obj) {
        return true;

      if (!(obj instanceof KeyAndSource)) {
        return false;

      KeyAndSource other = (KeyAndSource) obj;
      return Objects.equal(key, other.key)
          && Objects.equal(source, other.source);

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