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Java example source code file (ConcurrentHashMap.java)

This example Java source code file (ConcurrentHashMap.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

abstractmap, concurrenthashmap, concurrentmap, enumeration, nullpointerexception, object, override, set, util

The ConcurrentHashMap.java Java example source code

/*
 * Copyright (C) 2009 The Guava Authors
 *
 * 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 java.util.concurrent;

import java.util.AbstractMap;
import java.util.Collections;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;

/**
 * Minimal emulation of {@link java.util.concurrent.ConcurrentHashMap}.
 * Note that javascript intepreter is <a
 * href="http://code.google.com/docreader/#p=google-web-toolkit-doc-1-5&t=DevGuideJavaCompatibility">
 * single-threaded</a>, it is essentially a {@link java.util.HashMap},
 * implementing the new methods introduced by {@link ConcurrentMap}.
 *
 * @author Hayward Chan
 */
public class ConcurrentHashMap<K, V>
    extends AbstractMap<K, V> implements ConcurrentMap {

  private final Map<K, V> backingMap;

  public ConcurrentHashMap() {
    this.backingMap = new HashMap<K, V>();
  }

  public ConcurrentHashMap(int initialCapacity) {
    this.backingMap = new HashMap<K, V>(initialCapacity);
  }

  public ConcurrentHashMap(int initialCapacity, float loadFactor) {
    this.backingMap = new HashMap<K, V>(initialCapacity, loadFactor);
  }

  public ConcurrentHashMap(Map<? extends K, ? extends V> t) {
    this.backingMap = new HashMap<K, V>(t);
  }

  public V putIfAbsent(K key, V value) {
    if (!containsKey(key)) {
      return put(key, value);
    } else {
      return get(key);
    }
  }

  public boolean remove(Object key, Object value) {
    if (containsKey(key) && get(key).equals(value)) {
      remove(key);
      return true;
    } else {
      return false;
    }
  }

  public boolean replace(K key, V oldValue, V newValue) {
    if (oldValue == null || newValue == null) {
      throw new NullPointerException();
    } else if (containsKey(key) && get(key).equals(oldValue)) {
      put(key, newValue);
      return true;
    } else {
      return false;
    }
  }

  public V replace(K key, V value) {
    if (value == null) {
      throw new NullPointerException();
    } else if (containsKey(key)) {
      return put(key, value);
    } else {
      return null;
    }
  }

  @Override public boolean containsKey(Object key) {
    if (key == null) {
      throw new NullPointerException();
    }
    return backingMap.containsKey(key);
  }

  @Override public V get(Object key) {
    if (key == null) {
      throw new NullPointerException();
    }
    return backingMap.get(key);
  }

  @Override public V put(K key, V value) {
    if (key == null || value == null) {
      throw new NullPointerException();
    }
    return backingMap.put(key, value);
  }

  @Override public boolean containsValue(Object value) {
    if (value == null) {
      throw new NullPointerException();
    }
    return backingMap.containsValue(value);
  }

  @Override public V remove(Object key) {
    if (key == null) {
      throw new NullPointerException();
    }
    return backingMap.remove(key);
  }

  @Override public Set<Entry entrySet() {
    return backingMap.entrySet();
  }

  public boolean contains(Object value) {
    return containsValue(value);
  }

  public Enumeration<V> elements() {
    return Collections.enumeration(values());
  }

  public Enumeration<K> keys() {
    return Collections.enumeration(keySet());
  }
}

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