Design Pattern series-Observer

I. Class Diagram

 

Ii. Intention

Define a one-to-many dependency between objects,When the status of an object changes,All objects dependent on it are notified and automatically updated.

Iii. Applicability

A) When an abstract model has two aspects:,One aspect depends on the other. Encapsulate the two in independent objects so that they can be changed and reused independently.

B) when changing an object, you need to change other objects at the same time.,I don't know how many objects need to be changed.

C) when an object must notify other objects, it cannot assume who the other objects are. In other words,You do not want these objects to be tightly coupled.

Iv. Instances

In the fifth part of rural love, zhongda has come up with an idea. When Yang came, the security guard stopped Yang and informed Wang danale. I will not elaborate on the details. If you want to view the details online, you can. This is a typical observerDesign mode.

 

 Package Using e. observer;

 Public   Interface Observer {
 Public   Void Notice ();
}

 Package Using e. observer;
 //  Observer object 
  Public   Class Guardleader Implements Observer {
@ Override
 Public   Void Notice (){
System. Out. println ("Wang Zong, Yang Zong! ");
}
}

 Package Using e. observer;
 //  Observer object  
 Public   Class Guardmember Implements Observer {
@ Override
 Public   Void Notice (){
System. Out. println ("Yang has been here for 10 minutes ...");
}
}

 Package Using e. observer;

 Public   Interface Observable {
 Public  Void Addobserver (Observer O );
 Public   Void Delobserver (Observer O );
 Public   Void Inform ();
}

 Package Using e. observer;

 Import Java. util. arraylist;
 Import Java. util. List;

 //  Observable object 
  Public   Class Gate Implements Observable {
 Public List <observer> guards = Null ;

 Public Gate (){
Guards = New Arraylist <observer> ();
}

 Public   Void Openthegate (string person ){
If ("Yang Zong". Equals (person )){
Inform ();
}
System. Out. println ("Welcome, Mr. Yang! ");
}

@ Override
 Public   Void Addobserver (Observer O ){
Guards. Add (O );
}

@ Override
 Public   Void Delobserver (Observer O ){
Guards. Remove (O );
}

@ Override
 Public   Void Inform (){
 For (Observer O: Guards ){
O. Notice ();
}

}
}

 Package Using e. observer;

 Public   Class Client {
 Public   Static   Void Main (string [] ARGs ){
Guardleader leader = New Guardleader ();
Guardmember member = New Guardmember ();
Gate = New Gate ();
Gate. addobserver (leader );
Gate. addobserver (member );
Gate. openthegate ("Yang Zong ");
}
}

 

ThisObserverThe mode is customized.CodeAt the same timeJDKGiven inObserverThe implementation interfaces of areObservableAndObserver. I will not talk about the usage of these two classes. Please try to read them.APIRight.

 

5. AWTMediumObserverMode

 

Java AWTUsed in packageObserverThe mode is the most, and the image is written.ProgramAll know: we need to haveObserverClass listening, otherwise it will not produce the expected results.

 

Take a lookButtonClass source code:

 

 Public   Class Button Extends Component Implements Accessible {
......
 Public  Synchronized   Void Addactionlistener (actionlistener L ){
 If (L = Null ){
 Return ;
}
Actionlistener = awteventmulticaster. Add (actionlistener, L );
Neweventsonly = True ;
}

 Public   Synchronized   Void Removeactionlistener (actionlistener L ){
 If (L = Null ){
 Return ;
}
Actionlistener = awteventmulticaster. Remove (actionlistener, L );
}

 Protected   Void Processactionevent (actionevent e ){
Actionlistener listener = actionlistener;
 If (Listener! = Null ){
Listener. actionreceivmed (E );
}
}