Lecture 14

Lecture Topic:

Observers and Observable
Parent and Super Classes
Quiz

Observer and Observable

Java has a model-view paradigm. In this model, an observable object has to have the ability to maintain and update a list of interested observers. Observers implement observer interface when it wants to be informed if observable objects change.

(1). To maintain a list of observers, observers have to register 
themselves by calling:
 
          Observable.addObserver(this);
 
(2). The observable object will notify the observers by calling
 
          Observable.notifyObservers();
 
 
(3). Observers must implement the Update() method in order to get updated.
 
 
An observable object can have one or more observers.  After an observable 
instance changes, an application calling the Observerable's notifyObservers 
method causes all of its observers to be notified of the change by a call to 
their update method.

Parent and Super Classes

Parent is the superior container.
Super is an ancestor class.

Example:
 
	class a_frame extends Frame {
			P p_pane = new P();
			...;
			}
 
	class P extends Pane {
			Parent.press();		// refer to frame container
			Super.hide();		// refer to Pane base class
			parent.hide();		// refer to frame container
			}

Sample Quiz

1 An observable class can be subclassed to represent an object that the 
application wants to have observed. 
  a. TRUE
  b. FALSE
 
2. Super class is the base class of derived classes?
  a. TRUE.
  b. FALSE.
 
3. Parent class can contain other classes as though they are its property?
  a. TRUE.
  b. FALSE.