Using cajo Multicasting

This page is the result of questions regarding the use of the gnu.cajo.utils.Multicast class.

Here we will set out a simple two-class example, which will hopefully make its use clear. Both classes can be run on the same machine, or separate ones.

The first class is called Testee.java; it listens for a multicast announcement:

import gnu.cajo.utils.Multicast;

public class Testee {
   static Object object = new Testee();
   public Object multicast(Multicast m) { // multicast listener callback
      try { System.out.println(m.item.invoke("doit", "hello!")); }
      catch (Exception x)  { x.printStackTrace(); }
      synchronized(this) { notify(); } // end program
      return this; // stop listening, else return null
   }
   public static void main(String args[]) throws Exception { // unit test
      Multicast m = new Multicast();
      m.listen(object);
      synchronized(object) { object.wait(); }
   }
}

It should be running before starting the second example class; Tester.java:

import gnu.cajo.utils.Multicast;

public class Tester {
   static Object object = new Tester();
   public String doit(String message) { // remotely callable method
      System.out.println("Doing it " + message);
      synchronized(this) { notify(); } // end program
      return "Didit!";
   }
   public static void main(String args[]) throws Exception { // unit test
      Multicast m = new Multicast();
      m.announce(object, 3); // broadcast reference short distance
      synchronized(object) { object.wait(); }
      System.exit(0);
   }
}

To compile and run the Testee class, use the following command lines:

javac -classpath cajo.jar Testee.java

java -classpath cajo.jar;. Testee

javac -classpath cajo.jar Tester.java

java -classpath cajo.jar;. Tester

Tester will make a multicast announcement of a reference to its object. Testee will receive this reference, and invoke its doit method. This will result in the Teser object object printing the following line to its console:

Doing it hello!

This will effectively end the execution of Tester. However, not before its remotely callable method returns a String; this will cause Testee to print the following line to its console:

Didit!

Then it will terminate its execution as well.