Made RandomDataImpl consistently use a Well generator as the default random generator. This completes the fix for JIRA: MATH-701. The inconsistency was reported by Dennis Hendriks in JIRA: MATH-720.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/math/trunk@1213130 13f79535-47bb-0310-9956-ffa450edef68

src/main/java/org/apache/commons/math/random/RandomDataImpl.java

@@ -157,7 +157,12 @@ public class RandomDataImpl implements RandomData, Serializable {
     }
 
     /**
-     * Construct a RandomDataImpl.
+     * Construct a RandomDataImpl, using a default random generator as the source
+     * of randomness.
+     *
+     * <p>The default generator is a {@link Well19937c} seeded
+     * with {@code System.currentTimeMillis() + System.identityHashCode(this))}.
+     * The generator is initialized and seeded on first use.</p>
      */
     public RandomDataImpl() {
     }
@@ -167,7 +172,7 @@ public class RandomDataImpl implements RandomData, Serializable {
      * the source of (non-secure) random data.
      *
      * @param rand the source of (non-secure) random data
-     * (may be null, resulting in default JDK-supplied generator)
+     * (may be null, resulting in the default generator)
      * @since 1.1
      */
     public RandomDataImpl(RandomGenerator rand) {
@@ -836,11 +841,19 @@ public class RandomDataImpl implements RandomData, Serializable {
      */
     private RandomGenerator getRan() {
         if (rand == null) {
-            rand = new Well19937c(System.currentTimeMillis() + System.identityHashCode(this));
+            initRan();
         }
         return rand;
     }
 
+    /**
+     * Sets the default generator to a {@link Well19937c} generator seeded with
+     * {@code System.currentTimeMillis() + System.identityHashCode(this))}.
+     */
+    private void initRan() {
+        rand = new Well19937c(System.currentTimeMillis() + System.identityHashCode(this));
+    }
+
     /**
      * Returns the SecureRandom used to generate secure random data.
      * <p>
@@ -869,7 +882,7 @@ public class RandomDataImpl implements RandomData, Serializable {
      */
     public void reSeed(long seed) {
         if (rand == null) {
-            rand = new JDKRandomGenerator();
+            initRan();
         }
         rand.setSeed(seed);
     }
@@ -905,14 +918,14 @@ public class RandomDataImpl implements RandomData, Serializable {
     }
 
     /**
-     * Reseeds the random number generator with the current time in
-     * milliseconds.
+     * Reseeds the random number generator with
+     * {@code System.currentTimeMillis() + System.identityHashCode(this))}.
      */
     public void reSeed() {
         if (rand == null) {
-            rand = new JDKRandomGenerator();
+            initRan();
         }
-        rand.setSeed(System.currentTimeMillis());
+        rand.setSeed(System.currentTimeMillis() + System.identityHashCode(this));
     }
 
     /**

src/test/java/org/apache/commons/math/random/RandomDataTest.java

@@ -1056,5 +1056,18 @@ public class RandomDataTest {
         }
         TestUtils.assertChiSquareAccept(densityPoints, expectedCounts, observedCounts, .001);
     }
+    
+    @Test
+    /**
+     * MATH-720
+     */
+    public void testReseed() {
+        PoissonDistribution x = new PoissonDistribution(3.0);
+        x.reseedRandomGenerator(0);
+        final double u = x.sample();
+        PoissonDistribution y = new PoissonDistribution(3.0);
+        y.reseedRandomGenerator(0);
+        Assert.assertEquals(u, y.sample(), 0);
+    }
 
 }