The beta version of reactive programming is the traditional pub/sub app. It seems plausible that two instances of the same class may want to be in a pub/sub relationship so I wanted to code a class that would provide that.

PubSubApp.java

package com.frisco.pubsub;
import java.util.Observable;
import java.util.Observer;

public class PubSubApp extends Observable implements Observer {
	String name;
	PubSubApp(String name) {
		this.name = name;
		this.setChanged();
	}
	
	@Override
	public void update(Observable observable, Object arg) {
		System.out.println( "this=      " + this.name );
		System.out.println( "observable=" + ((PubSubApp)observable).name );
	}
	
	public static void main(String[] args) {
		Observable observable = new PubSubApp("observable");
		Observer observer1 = new PubSubApp("observer1");
		Observer observer2 = new PubSubApp("observer2");
		observable.addObserver(observer1);
		observable.addObserver(observer2);
		System.out.println("count=" + observable.countObservers());
		observable.notifyObservers();
	}
}

results

count=2
this=      observer2
observable=observable
this=      observer1
observable=observable