use Java Subject<T, R> as contravariant in T and covariant in R

Author: samuelgruetter

rxjava-core/src/main/java/rx/Observable.java

@@ -397,7 +397,7 @@ public Subscription subscribe(final Action1<? super T> onNext, final Action1<Thr
      * @return a {@link ConnectableObservable} that upon connection causes the source Observable to
      *         push results into the specified {@link Subject}
      */
-    public <R> ConnectableObservable<R> multicast(Subject<T, R> subject) {
+    public <R> ConnectableObservable<R> multicast(Subject<? super T, ? extends R> subject) {
         return OperationMulticast.multicast(this, subject);
     }
 

rxjava-core/src/main/java/rx/operators/OperationMulticast.java

@@ -27,19 +27,19 @@
 import rx.subjects.Subject;
 
 public class OperationMulticast {
-    public static <T, R> ConnectableObservable<R> multicast(Observable<? extends T> source, final Subject<T, R> subject) {
+    public static <T, R> ConnectableObservable<R> multicast(Observable<? extends T> source, final Subject<? super T, ? extends R> subject) {
         return new MulticastConnectableObservable<T, R>(source, subject);
     }
 
     private static class MulticastConnectableObservable<T, R> extends ConnectableObservable<R> {
         private final Object lock = new Object();
 
         private final Observable<? extends T> source;
-        private final Subject<T, R> subject;
+        private final Subject<? super T, ? extends R> subject;
 
         private Subscription subscription;
 
-        public MulticastConnectableObservable(Observable<? extends T> source, final Subject<T, R> subject) {
+        public MulticastConnectableObservable(Observable<? extends T> source, final Subject<? super T, ? extends R> subject) {
             super(new OnSubscribeFunc<R>() {
                 @Override
                 public Subscription onSubscribe(Observer<? super R> observer) {