/*

 * 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

 * <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

     * <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

     * <pre>

     *   if (map.containsKey(key) && 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

     *         (<a href="../Collection.html#optional-restrictions">optional</a>)

     * @throws NullPointerException if the specified key or value is null,

     *         and this map does not permit null keys or values

     *         (<a href="../Collection.html#optional-restrictions">optional</a>)

     */

    boolean remove(Object key, Object value);

    /**

     * Replaces the entry for a key only if currently mapped to a given value.

     * This is equivalent to

     * <pre>

     *   if (map.containsKey(key) && 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

     * <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);

}