add exists and isEmpty

Author: samuelgruetter

language-adaptors/rxjava-scala/src/examples/scala/rx/lang/scala/examples/RxScalaDemo.scala

@@ -411,6 +411,15 @@ class RxScalaDemo extends JUnitSuite {
     })
   }
 
+  @Test def elementAtReplacement() {
+    assertEquals("b", Observable("a", "b", "c").drop(1).first.toBlockingObservable.single)
+  }
+  
+  @Test def elementAtOrDefaultReplacement() {
+    assertEquals("b", Observable("a", "b", "c").drop(1).firstOrElse("!").toBlockingObservable.single)
+    assertEquals("!!", Observable("a", "b", "c").drop(10).firstOrElse("!!").toBlockingObservable.single)
+  }
+  
   def output(s: String): Unit = println(s)
 
   // blocks until obs has completed

language-adaptors/rxjava-scala/src/main/scala/rx/lang/scala/Observable.scala

@@ -1749,7 +1749,26 @@ class Observable[+T] private[scala] (val asJava: rx.Observable[_ <: T])
     val fJava: Func1[rx.Observable[T], rx.Observable[R]] =
       (jo: rx.Observable[T]) => f(Observable[T](jo)).asJava.asInstanceOf[rx.Observable[R]]
     Observable[R](asJava.asInstanceOf[rx.Observable[T]].parallel[R](fJava, scheduler))
-  }  
+  }
+
+  /** Tests whether a predicate holds for some of the elements of this `Observable`.
+   *
+   *  @param   p     the predicate used to test elements.
+   *  @return        an Observable emitting one single Boolean, which is `true` if the given predicate `p` 
+   *                 holds for some of the elements of this Observable, and `false` otherwise.
+   */
+  def exists(p: T => Boolean): Observable[Boolean] = {
+    Observable[java.lang.Boolean](asJava.exists(p)).map(_.booleanValue())
+  }
+
+  /** Tests whether this `Observable` emits no elements.
+   *
+   *  @return        an Observable emitting one single Boolean, which is `true` if this `Observable` 
+   *                 emits no elements, and `false` otherwise.
+   */
+  def isEmpty: Observable[Boolean] = {
+    Observable[java.lang.Boolean](asJava.isEmpty).map(_.booleanValue())
+  }
 
   def withFilter(p: T => Boolean): WithFilter[T] = {
     new WithFilter[T](p, asJava)

language-adaptors/rxjava-scala/src/test/scala/rx/lang/scala/CompletenessTest.scala

@@ -31,7 +31,9 @@ class CompletenessTest extends JUnitSuite {
       "buffer(Long, Long, TimeUnit)" -> "buffer(Duration, Duration)",
       "buffer(Long, Long, TimeUnit, Scheduler)" -> "buffer(Duration, Duration, Scheduler)",
       "count()" -> "length",
-      "dematerialize()" -> "dematerialize(<:<[T, Notification[U]])",
+      "dematerialize()" -> "dematerialize(<:<[Observable[T], Observable[Notification[U]]])",
+      "elementAt(Int)" -> "[use `.drop(index).first`]",
+      "elementAtOrDefault(Int, T)" -> "[use `.drop(index).firstOrElse(default)`]",
       "first(Func1[_ >: T, Boolean])" -> commentForFirstWithPredicate,
       "firstOrDefault(T)" -> "firstOrElse(=> U)", 
       "firstOrDefault(Func1[_ >: T, Boolean], T)" -> "[use `.filter(condition).firstOrElse(default)`]",