Introduce Subject as analogue to RX ISubject

Author: johngmyers

rxjava-core/src/main/java/rx/subjects/PublishSubject.java

@@ -19,7 +19,7 @@
 import rx.util.functions.Action1;
 import rx.util.functions.Func1;
 
-public class PublishSubject<T> extends Observable<T> implements Observer<T> {
+public class PublishSubject<T> extends Subject<T, T> {
     public static <T> PublishSubject<T> create() {
         final ConcurrentHashMap<Subscription, Observer<T>> observers = new ConcurrentHashMap<Subscription, Observer<T>>();
 

rxjava-core/src/main/java/rx/subjects/Subject.java

@@ -0,0 +1,18 @@
+package rx.subjects;
+
+import rx.Observable;
+import rx.Observer;
+import rx.Subscription;
+import rx.util.functions.Func1;
+
+public abstract class Subject<I, O> extends Observable<O> implements Observer<I> {
+    protected Subject()
+    {
+        super();
+    }
+
+    protected Subject(Func1<Observer<O>, Subscription> onSubscribe)
+    {
+        super(onSubscribe);
+    }
+}