Update Java STM API to include STM utils

akka-stm/src/test/java/akka/stm/example/RetryExample.java

@@ -0,0 +1,47 @@
+package akka.stm.example;
+
+import akka.stm.*;
+import akka.actor.*;
+
+public class RetryExample {
+    public static void main(String[] args) {
+        System.out.println();
+        System.out.println("Retry example");
+        System.out.println();
+
+        final Ref<Double> account1 = new Ref<Double>(100.0);
+        final Ref<Double> account2 = new Ref<Double>(100.0);
+
+        ActorRef transferer = Actors.actorOf(Transferer.class).start();
+
+        transferer.sendOneWay(new Transfer(account1, account2, 500.0));
+        // Transferer: not enough money - retrying
+
+        new Atomic() {
+            public Object atomically() {
+                return account1.set(account1.get() + 2000);
+            }
+        }.execute();
+        // Transferer: transferring
+
+        Double acc1 = new Atomic<Double>() {
+            public Double atomically() {
+                return account1.get();
+            }
+        }.execute();
+
+        Double acc2 = new Atomic<Double>() {
+            public Double atomically() {
+                return account2.get();
+            }
+        }.execute();
+
+        System.out.println("Account 1: " + acc1);
+        // Account 1: 1600.0
+
+        System.out.println("Account 2: " + acc2);
+        // Account 2: 600.0
+
+        transferer.stop();
+    }
+}