!cdd #17770 Use self recursive type in AbstractReplicatedData (Java API)

* complete the TwoPhaseSet java sample with serialization

akka-docs/rst/java/code/docs/ddata/japi/TwoPhaseSet.java

@@ -0,0 +1,48 @@
+/**
+ * Copyright (C) 2015 Typesafe Inc. <http://www.typesafe.com>
+ */
+package docs.ddata.japi;
+
+import java.util.HashSet;
+
+import java.util.Set;
+
+import akka.cluster.ddata.AbstractReplicatedData;
+import akka.cluster.ddata.GSet;
+
+//#twophaseset
+public class TwoPhaseSet extends AbstractReplicatedData<TwoPhaseSet> {
+  
+  public final GSet<String> adds;
+  public final GSet<String> removals;
+  
+  public TwoPhaseSet(GSet<String> adds, GSet<String> removals) {
+    this.adds = adds;
+    this.removals = removals;
+  }
+  
+  public static TwoPhaseSet create() {
+    return new TwoPhaseSet(GSet.create(), GSet.create());
+  }
+
+  public TwoPhaseSet add(String element) {
+    return new TwoPhaseSet(adds.add(element), removals);
+  }
+  
+  public TwoPhaseSet remove(String element) {
+    return new TwoPhaseSet(adds, removals.add(element));
+  }
+
+  public Set<String> getElements() {
+    Set<String> result = new HashSet<>(adds.getElements());
+    result.removeAll(removals.getElements());
+    return result;
+  }
+
+  @Override
+  public TwoPhaseSet mergeData(TwoPhaseSet that) {
+    return new TwoPhaseSet(this.adds.merge(that.adds), 
+        this.removals.merge(that.removals));
+  }
+}
+//#twophaseset