src/share/classes/java/util/concurrent/ConcurrentMap.java

rev 6878 : 8004518: Add in-place operations to Map
8010122: Add defaults for ConcurrentMap operations to Map
Reviewed-by: darcy, briangoetz, mduigou, dholmes, ulfzibis
Contributed-by: Doug Lea <dl at cs.oswego.edu>, Henry Jen <henry.jen@oracle.com>, Akhil Arora <akhil.arora@oracle.com>, Peter Levart <peter.levart@gmail.com>

@@ -36,11 +36,11 @@
 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.
+ * {@code putIfAbsent}, {@code remove}, and {@code replace} 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>

@@ -55,10 +55,25 @@
  * @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> {
+
+    /**
+     * {@inheritDoc}
+     *
+     * @implNote This implementation assumes that the ConcurrentMap cannot
+     * contain null values and get() returning null unambiguously means the key
+     * is absent. Implementations which support null values must override this
+     * default implementation.
+     */
+    @Override
+    default V getOrDefault(Object key, V defaultValue) {
+        V v;
+        return ((v = get(key)) != null) ? v : defaultValue;
+    }
+
     /**
      * If the specified key is not already associated
      * with a value, associate it with the given value.
      * This is equivalent to
      *  <pre> {@code

@@ -89,22 +104,22 @@
 
     /**
      * Removes the entry for a key only if currently mapped to a given value.
      * This is equivalent to
      *  <pre> {@code
-     * if (map.containsKey(key) && map.get(key).equals(value)) {
+     * if (map.containsKey(key) && Objects.equals(map.get(key), 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
+     * @return {@code true} if the value was removed
+     * @throws UnsupportedOperationException if the {@code remove} 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,

@@ -115,23 +130,23 @@
 
     /**
      * Replaces the entry for a key only if currently mapped to a given value.
      * This is equivalent to
      *  <pre> {@code
-     * if (map.containsKey(key) && map.get(key).equals(oldValue)) {
+     * if (map.containsKey(key) && Objects.equals(map.get(key), 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
+     * @return {@code true} if the value was replaced
+     * @throws UnsupportedOperationException if the {@code 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

@@ -152,15 +167,15 @@
      * 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,
+     *         {@code null} if there was no mapping for the key.
+     *         (A {@code null} return can also indicate that the map
+     *         previously associated {@code null} with the key,
      *         if the implementation supports null values.)
-     * @throws UnsupportedOperationException if the <tt>put</tt> operation
+     * @throws UnsupportedOperationException if the {@code 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