Fix the docs for the no-arg Random() constructor to better reflect reality,

and make the constructors more resilient with respect to subclassing by
using System.identityHashCode() instead of Object.hashCode(), and also by
not calling overridable methods.

Change-Id: I6239d93bb46876ef1c4a5e155a6dc1ac6fab4eae

diff --git a/libcore/luni/src/main/java/java/util/Random.java b/libcore/luni/src/main/java/java/util/Random.java
index be27258..f893020 100644 (file)
--- a/libcore/luni/src/main/java/java/util/Random.java
+++ b/libcore/luni/src/main/java/java/util/Random.java
@@ -52,15 +52,22 @@ public class Random implements Serializable {
      */
     private double nextNextGaussian;
 
+    // BEGIN android-changed
     /**
-     * Construct a random generator with the current time of day in milliseconds
-     * as the initial state.
+     * Constructs a random generator with an initial state that is
+     * unlikely to be duplicated by a subsequent instantiation.
+     *
+     * <p>The initial state (that is, the seed) is <i>partially</i> based
+     * on the current time of day in milliseconds.</p>
      * 
      * @see #setSeed
      */
     public Random() {
-        setSeed(System.currentTimeMillis() + hashCode());
+        // Note: Using identityHashCode() to be hermetic wrt subclasses.
+        internalSetSeed(
+                System.currentTimeMillis() + System.identityHashCode(this));
     }
+    // END android-changed
 
     /**
      * Construct a random generator with the given {@code seed} as the
@@ -72,7 +79,9 @@ public class Random implements Serializable {
      * @see #setSeed
      */
     public Random(long seed) {
-        setSeed(seed);
+        // BEGIN android-changed
+        internalSetSeed(seed);
+        // END android-changed
     }
 
     /**
@@ -236,6 +245,7 @@ public class Random implements Serializable {
         return ((long) next(32) << 32) + next(32);
     }
 
+    // BEGIN android-changed
     /**
      * Modifies the seed a using linear congruential formula presented in <i>The
      * Art of Computer Programming, Volume 2</i>, Section 3.2.1.
@@ -247,7 +257,20 @@ public class Random implements Serializable {
      * @see #Random(long)
      */
     public synchronized void setSeed(long seed) {
+        internalSetSeed(seed);
+    }
+
+    /**
+     * Sets the seed. This is used both in the constructor and in the
+     * default implementation of {@link #setSeed}.
+     *
+     * @param seed
+     *            the seed that alters the state of the random number
+     *            generator.
+     */
+    private void internalSetSeed(long seed) {
         this.seed = (seed ^ multiplier) & ((1L << 48) - 1);
         haveNextNextGaussian = false;
     }
+    // END android-changed
 }