Prevent direct instantiation of BlockingObservable via no-arg constructor

- also questioning why to allow extending this and would like to make it a private constructor

Author: benjchristensen

rxjava-core/src/main/java/rx/observables/BlockingObservable.java

@@ -44,6 +44,18 @@
  */
 public class BlockingObservable<T> extends Observable<T> {
 
+    protected BlockingObservable(Func1<Observer<T>, Subscription> onSubscribe) {
+        super(onSubscribe);
+    }
+    
+    /**
+     * Used to prevent public instantiation
+     */
+    @SuppressWarnings("unused")
+    private BlockingObservable() {
+        // prevent public instantiation
+    }
+    
     public static <T> BlockingObservable<T> from(final Observable<T> o) {
         return new BlockingObservable<T>(new Func1<Observer<T>, Subscription>() {
 
@@ -330,10 +342,6 @@ public static <T> Iterable<T> toIterable(final Observable<T> source) {
         return from(source).toIterable();
     }
 
-    protected BlockingObservable(Func1<Observer<T>, Subscription> onSubscribe) {
-        super(onSubscribe);
-    }
-
     /**
      * Used for protecting against errors being thrown from Observer implementations and ensuring onNext/onError/onCompleted contract compliance.
      * <p>