Check out example codes for "observer pattern java". It will help you in understanding the concepts better.

Code Example 1

class Signal extends Observable {

  void setData(byte[] lbData){
    setChanged(); // Positionne son indicateur de changement
    notifyObservers(); // (1) notification
  }
}

Code Example 2

class JPanelSignal extends JPanel implements Observer {

  void init(Signal lSigAObserver) {
    lSigAObserver.addObserver(this); // (2) ajout d'observateur
  }

  void update(Observable observable, Object objectConcerne) {
    repaint();  // (3) traitement de l'observation
  }
}

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