/* * 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 * or visit www.oracle.com if you need additional information or have any * questions. */ /* * 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/publicdomain/zero/1.0/ */ package java.util.concurrent; import java.util.Map; /** * A {@link java.util.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 * {@code ConcurrentMap} as a key or value * happen-before * actions subsequent to the access or removal of that object from * the {@code ConcurrentMap} in another thread. * *

This interface is a member of the * * Java Collections Framework. * * @since 1.5 * @author Doug Lea * @param the type of keys maintained by this map * @param the type of mapped values */ public interface ConcurrentMap extends Map { /** * {@inheritDoc} * * @implNote This implementation assumes that the ConcurrentMap cannot * contain null values and get() returning null unambiguously means no * mapping is present. Implementations which support null values must * override this default implementation. */ @Override default V getOrDefault(Object key, V defaultValue) { V v; return (null != (v = get(key))) ? v : defaultValue; } /** * If the specified key is not already associated * with a value, associate it with the given value. * This is equivalent to * 

 {@code
     * if (!map.containsKey(key))
     *   return map.put(key, value);
     * else
     *   return map.get(key);}
* * 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 * 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.) * @throws UnsupportedOperationException if the put 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 * 
 {@code
     * if (map.containsKey(key) && map.get(key).equals(value)) {
     *   map.remove(key);
     *   return true;
     * } else
     *   return false;}
* * 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 true if the value was removed * @throws UnsupportedOperationException if the remove 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 * 
 {@code
     * 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. * * @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 true if the value was replaced * @throws UnsupportedOperationException if the put 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 * 
 {@code
     * if (map.containsKey(key)) {
     *   return map.put(key, value);
     * } else
     *   return null;}
* * 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 * 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.) * @throws UnsupportedOperationException if the put 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); }