java-design Pattern (behavioral)-"Viewer mode"

1. Observer pattern (Observer mode)

Definition: A one-to-many relationship that belongs to a relationship between classes and classes, and does not involve inheritance.

When an object changes , other objects that depend on the object are notified and will change !

Diagram:

2. Examples of leaders informing students and teachers

2.1 Observers

Observer interface: Update method (update all subclasses) public interface Observer {     //update all observervoid update ();} Student Classes Class Student implements observer{   String name;   Public Student (String name)   {   this.name=name;   } @Overridepublic void Update () {//TODO auto-generated method StubSystem.out.println (name+ "Receive notification ... ");}} Teacher Class Teacher implements observer{string name;    Public Teacher (String name)    {    this.name=name;    } @Overridepublic void Update () {//TODO auto-generated method StubSystem.out.println (name+ "Receive notification ... ");}

2.2 Main body: Leader class

//body: Manage all observers and notify observers public abstract interface Subject {//Add Observer method void Addobserver (Observer OB);//delete observer method void Removeobserver (Observer ob);//Notify All observers void Notifyobservers ();} Leadership Class Leader implements subject{//pool for all observers: Thread synchronization class Vectorprivate vector<observer> vt=new vector<observer    > ();//Add observer @overridepublic void Addobserver (Observer ob) {//TODO auto-generated method Stubvt.add (OB);}    Delete Observer @overridepublic void Removeobserver (Observer ob) {//TODO auto-generated method Stubvt.remove (OB);} Notifies the Observer @overridepublic Void Notifyobservers () {//calls the Update method of each observer enumeration<observer> e=vt.elements (); System.out.print ("leader informs all subordinates:"); Getcurrentdate (); while (E.hasmoreelements ()) {Observer ob=e.nextelement (); ob.update ();}} Gets the current system time public void Getcurrentdate () {Calendar cal=calendar.getinstance ();    SimpleDateFormat sdf=new SimpleDateFormat ("Yyyy-mm-dd HH:mm:ss");    String Date=sdf.format (Cal.gettime ()); SYSTEM.OUT.PRINTLN (date);}} 

2.3 Testing

public class Test {public static void main (string[] args) {//TODO auto-generated method stub       Subject  leader=new L Eader ();       Student stu1=new Student ("Zhang students");       Teacher t1=new Teacher ("Miss Li");       Added into the Observer pool       Leader.addobserver (STU1);       Leader.addobserver (t1);       Notify all observers       leader.notifyobservers ();}}

2.4 Running Results

The leader informs all subordinates: 2015-04-20 11:22:06 student receives the notice ... Miss Li received the notice ...

　　

java-design Pattern (behavioral)-"Viewer mode"