Implementing a Simple Event Notifier

In this section, you will learn how to implement a Simple Event Notifier.

The Observer and Observable classes are useful for implementing a simple event notifier. The Observer class informed the changes that occurred in observable objects and Observable class represents an object that the application wants to have observed. You can see in the given example, the setChanged() protected method marks the Observable object as having been changed. If this object has changed, then notify all of its observers using the protected method notifyObservers(Object args) passing object type parameter. The method update(Observable o, Object arg) is called whenever the observed object is changed. When you call the method my.setChanged(), it will indicate that the model has changed. Then the event is fired displaying the updated argument.

Here is the code of SimpleEventNotifier.java


import java.util.*;

class MyClass extends Observable {

  public synchronized void setChanged() {

  super.setChanged();

  }

  public synchronized void notifyObservers(Object args){

  System.out.println(args);

  }

  }

  public class SimpleEventNotifier{

  public static void main(String[]args){

  MyClass my = new MyClass();

  my.addObserver(new Observer() {

  public void update(Observable o, Object arg) {

  }

  });

  my.setChanged();

  Object arg = "Event is fired";

  my.notifyObservers(arg);

}

}

Output will be displayed as:

Download Source Code:

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