src/java.base/share/classes/java/lang/ref/SoftReference.java

@@ -24,14 +24,18 @@
   */
  
  package java.lang.ref;
  
  
+ import java.util.Objects;
+ 
  /**
   * Soft reference objects, which are cleared at the discretion of the garbage
   * collector in response to memory demand.  Soft references are most often used
   * to implement memory-sensitive caches.
+  * <p>
+  * The referent must be an {@linkplain Objects#isIdentityObject(Object) identity object}.
   *
   * <p> Suppose that the garbage collector determines at a certain point in time
   * that an object is <a href="package-summary.html#reachability">softly
   * reachable</a>.  At that time it may choose to clear atomically all soft
   * references to that object and all soft references to any other

@@ -79,10 +83,12 @@
      /**
       * Creates a new soft reference that refers to the given object.  The new
       * reference is not registered with any queue.
       *
       * @param referent object the new soft reference will refer to
+      * @throws IdentityException if the referent is not an
+      *         {@link java.util.Objects#isIdentityObject(Object) identity object}
       */
      public SoftReference(T referent) {
          super(referent);
          this.timestamp = clock;
      }

@@ -92,11 +98,12 @@
       * registered with the given queue.
       *
       * @param referent object the new soft reference will refer to
       * @param q the queue with which the reference is to be registered,
       *          or {@code null} if registration is not required
-      *
+      * @throws IdentityException if the referent is not an
+      *         {@link java.util.Objects#isIdentityObject(Object) identity object}
       */
      public SoftReference(T referent, ReferenceQueue<? super T> q) {
          super(referent, q);
          this.timestamp = clock;
      }