Fixing #522

akka-actor/src/main/scala/actor/Actor.scala

@@ -413,8 +413,14 @@ trait Actor extends Logging {
   /**
    * Changes tha Actor's behavior to become the new 'Receive' (PartialFunction[Any, Unit]) handler.
    * Puts the behavior on top of the hotswap stack.
+   * If "discardOld" is true, an unbecome will be issued prior to pushing the new behavior to the stack
    */
-  def become(behavior: Receive): Unit = self.hotswap = self.hotswap.push(behavior)
+  def become(behavior: Receive, discardOld: Boolean = false) {
+    if (discardOld)
+      unbecome
+
+    self.hotswap = self.hotswap.push(behavior)
+  }
 
   /**
    * Reverts the Actor behavior to the previous one in the hotswap stack.

akka-actor/src/main/scala/actor/UntypedActor.scala

@@ -72,7 +72,13 @@ abstract class UntypedActor extends Actor {
   /**
    * Java API for become
    */
-  def become(behavior: Procedure[Any]): Unit = super.become { case msg => behavior.apply(msg) }
+  def become(behavior: Procedure[Any]):Unit = become(behavior,false)
+
+  /*
+   * Java API for become with optional discardOld
+   */
+  def become(behavior: Procedure[Any], discardOld: Boolean): Unit =
+    super.become({ case msg => behavior.apply(msg) }, discardOld)
 
   @throws(classOf[Exception])
   def onReceive(message: Any): Unit