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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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/*
 * This file is available under and governed by the GNU General Public
 * License version 2 only, as published by the Free Software Foundation.
 * However, the following notice accompanied the original version of this
 * file:
 *
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/licenses/publicdomain
 */

package java.util.concurrent;
import java.util.Map;


A Map providing additional atomic putIfAbsent, remove, and replace methods.

Memory consistency effects: As with other concurrent collections, actions in a thread prior to placing an object into a ConcurrentMap as a key or value happen-before actions subsequent to the access or removal of that object from the ConcurrentMap in another thread. 
This interface is a member of the

Java Collections Framework.

Author:Doug Lea
Type parameters:
  • <K> – the type of keys maintained by this map
  • <V> – the type of mapped values
Since:1.5
/**
 * A {@link java.util.Map} providing additional atomic
 * <tt>putIfAbsent</tt>, <tt>remove</tt>, and <tt>replace</tt> methods.
 *
 * <p>Memory consistency effects: As with other concurrent
 * collections, actions in a thread prior to placing an object into a
 * {@code ConcurrentMap} as a key or value
 * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
 * actions subsequent to the access or removal of that object from
 * the {@code ConcurrentMap} in another thread.
 *
 * <p>This interface is a member of the
 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @since 1.5
 * @author Doug Lea
 * @param <K> the type of keys maintained by this map
 * @param <V> the type of mapped values
 */
public interface ConcurrentMap<K, V> extends Map<K, V> {
    
If the specified key is not already associated
with a value, associate it with the given value.
This is equivalent to

  if (!map.containsKey(key))
      return map.put(key, value);
  else
      return map.get(key);

except that the action is performed atomically.

Params:
  • key – key with which the specified value is to be associated
  • value – value to be associated with the specified key
Throws:
Returns:the previous value associated with the specified key, or
        null if there was no mapping for the key.
        (A null return can also indicate that the map
        previously associated null with the key,
        if the implementation supports null values.)
/**
     * If the specified key is not already associated
     * with a value, associate it with the given value.
     * This is equivalent to
     * <pre>
     *   if (!map.containsKey(key))
     *       return map.put(key, value);
     *   else
     *       return map.get(key);</pre>
     * except that the action is performed atomically.
     *
     * @param key key with which the specified value is to be associated
     * @param value value to be associated with the specified key
     * @return the previous value associated with the specified key, or
     *         <tt>null</tt> if there was no mapping for the key.
     *         (A <tt>null</tt> return can also indicate that the map
     *         previously associated <tt>null</tt> with the key,
     *         if the implementation supports null values.)
     * @throws UnsupportedOperationException if the <tt>put</tt> operation
     *         is not supported by this map
     * @throws ClassCastException if the class of the specified key or value
     *         prevents it from being stored in this map
     * @throws NullPointerException if the specified key or value is null,
     *         and this map does not permit null keys or values
     * @throws IllegalArgumentException if some property of the specified key
     *         or value prevents it from being stored in this map
     *
     */
    V putIfAbsent(K key, V value);

    
Removes the entry for a key only if currently mapped to a given value.
This is equivalent to

  if (map.containsKey(key) && map.get(key).equals(value)) {
      map.remove(key);
      return true;
  } else return false;

except that the action is performed atomically.

Params:
  • key – key with which the specified value is associated
  • value – value expected to be associated with the specified key
Throws:
Returns:true if the value was removed
/**
     * Removes the entry for a key only if currently mapped to a given value.
     * This is equivalent to
     * <pre>
     *   if (map.containsKey(key) &amp;&amp; map.get(key).equals(value)) {
     *       map.remove(key);
     *       return true;
     *   } else return false;</pre>
     * except that the action is performed atomically.
     *
     * @param key key with which the specified value is associated
     * @param value value expected to be associated with the specified key
     * @return <tt>true</tt> if the value was removed
     * @throws UnsupportedOperationException if the <tt>remove</tt> operation
     *         is not supported by this map
     * @throws ClassCastException if the key or value is of an inappropriate
     *         type for this map (optional)
     * @throws NullPointerException if the specified key or value is null,
     *         and this map does not permit null keys or values (optional)
     */
    boolean remove(Object key, Object value);

    
Replaces the entry for a key only if currently mapped to a given value.
This is equivalent to

  if (map.containsKey(key) && map.get(key).equals(oldValue)) {
      map.put(key, newValue);
      return true;
  } else return false;

except that the action is performed atomically.

Params:
  • key – key with which the specified value is associated
  • oldValue – value expected to be associated with the specified key
  • newValue – value to be associated with the specified key
Throws:
Returns:true if the value was replaced
/**
     * Replaces the entry for a key only if currently mapped to a given value.
     * This is equivalent to
     * <pre>
     *   if (map.containsKey(key) &amp;&amp; map.get(key).equals(oldValue)) {
     *       map.put(key, newValue);
     *       return true;
     *   } else return false;</pre>
     * except that the action is performed atomically.
     *
     * @param key key with which the specified value is associated
     * @param oldValue value expected to be associated with the specified key
     * @param newValue value to be associated with the specified key
     * @return <tt>true</tt> if the value was replaced
     * @throws UnsupportedOperationException if the <tt>put</tt> operation
     *         is not supported by this map
     * @throws ClassCastException if the class of a specified key or value
     *         prevents it from being stored in this map
     * @throws NullPointerException if a specified key or value is null,
     *         and this map does not permit null keys or values
     * @throws IllegalArgumentException if some property of a specified key
     *         or value prevents it from being stored in this map
     */
    boolean replace(K key, V oldValue, V newValue);

    
Replaces the entry for a key only if currently mapped to some value.
This is equivalent to

  if (map.containsKey(key)) {
      return map.put(key, value);
  } else return null;

except that the action is performed atomically.

Params:
  • key – key with which the specified value is associated
  • value – value to be associated with the specified key
Throws:
Returns:the previous value associated with the specified key, or
        null if there was no mapping for the key.
        (A null return can also indicate that the map
        previously associated null with the key,
        if the implementation supports null values.)
/**
     * Replaces the entry for a key only if currently mapped to some value.
     * This is equivalent to
     * <pre>
     *   if (map.containsKey(key)) {
     *       return map.put(key, value);
     *   } else return null;</pre>
     * except that the action is performed atomically.
     *
     * @param key key with which the specified value is associated
     * @param value value to be associated with the specified key
     * @return the previous value associated with the specified key, or
     *         <tt>null</tt> if there was no mapping for the key.
     *         (A <tt>null</tt> return can also indicate that the map
     *         previously associated <tt>null</tt> with the key,
     *         if the implementation supports null values.)
     * @throws UnsupportedOperationException if the <tt>put</tt> operation
     *         is not supported by this map
     * @throws ClassCastException if the class of the specified key or value
     *         prevents it from being stored in this map
     * @throws NullPointerException if the specified key or value is null,
     *         and this map does not permit null keys or values
     * @throws IllegalArgumentException if some property of the specified key
     *         or value prevents it from being stored in this map
     */
    V replace(K key, V value);
}