Observer and Observable Example

In Java we have Observer interface and Observable class, Below program gives a sample use of Observer and Observable

import java.util.Observable;

public class Employee extends Observable {
 float salary;

 public void setSalary(float newSalary) {
  salary = newSalary; // salary has changed
  setChanged(); // mark that this object has changed, MANDATORY
  notifyObservers(new Float(salary)); // notify all observers, MANDATORY
 }
}

import java.util.Observable;
import java.util.Observer;

public class Manager implements Observer {

 public void update(Observable obj, Object arg) {
  System.out.println("A change has happened and new salary is " + arg);
 }
}


public class Demo {
 public static void main(String[] args) {
  Employee e = new Employee();
  Manager m = new Manager();
  e.addObserver(m); // register for observing
  for (int i = 0; i < 10; i++) {
   try {
    Thread.sleep(1000);
   } catch (InterruptedException e1) {
    e1.printStackTrace();
   }
   if (i == 5) {
    e.setSalary(100);
   }
  }
 }
}