1.1 --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
     1.2 +++ b/code/observer-example.java	Fri Aug 10 22:15:51 2007 +0200
     1.3 @@ -0,0 +1,31 @@
     1.4 +        import java.util.Observable;
     1.5 +        import java.util.Observer;
     1.6 +
     1.7 +        public class MessageBoard extends Observable {
     1.8 +          private String message;
     1.9 +
    1.10 +          public String getMessage() {
    1.11 +            return message;
    1.12 +          }
    1.13 +
    1.14 +          public void changeMessage(String message) {
    1.15 +            this.message = message;
    1.16 +            setChanged();
    1.17 +            notifyObservers(message);
    1.18 +          }
    1.19 +
    1.20 +          public static void main(String[] args) {
    1.21 +            MessageBoard board = new MessageBoard();
    1.22 +            Student bob = new Student();
    1.23 +            Student joe = new Student();
    1.24 +            board.addObserver(bob);
    1.25 +            board.addObserver(joe);
    1.26 +            board.changeMessage("More Homework!");
    1.27 +          }
    1.28 +        }
    1.29 +
    1.30 +        class Student implements Observer {
    1.31 +          public void update(Observable o, Object arg) {
    1.32 +            System.out.println("Message board changed: " + arg);
    1.33 +          }
    1.34 +        }