Contrary to the pull-style of channels, some building blocks provide an event-like push-style message delivery model. In this case, the entity to be notified of message reception needs to provide a callback to be invoked whenever a message has been received. The MessageListener interface (JavaGroups.MessageListener) below provides a method to do so:
public interface MessageListener {
public void Receive(Message msg);
}
Method Receive will be called when a message is received.