Design pattern Start--viewer mode

Observer pattern

One, the problem: Define a one-to-many dependency, so that multiple observers listen to a Subject object at the same time, when the subject object changes, will notify all the Observer object

Second, the role: When an object changes need to change other objects at the same time

Third, class diagram

(1) Type of push

(2) Form of pull

Iv. Realization OF

(1) Abstract Theme class

 Public Interface Isubject {    publicvoid  Register (iobserver observer);      Public void Unregister (IObserver observer);      Public void notifyobservers ();}

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(2) Specific subject categories

 Public classSubjectImplementsIsubject {PrivateVector<iobserver> VEC =NewVector<iobserver>(); PrivateString data;  PublicString GetData () {returndata; }     Public voidsetData (String data) { This. data =data; } @Override Public voidregister (IObserver observer) {VEC.ADD (Observer); } @Override Public voidUnregister (IObserver observer) {if(Vec.contains (Observer)) VEC.REMOVE (Observer); } @Override Public voidnotifyobservers () { for(inti = 0; I < vec.size (); i++) {vec.get (i). Refresh ( This); }    }}

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(3) Abstract Viewer class

 Public Interface IObserver {    publicvoid  refresh (isubject subject);}

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(4) Specific observer class

 Public class Implements iobserver {    @Override    publicvoid  refresh (isubject subject) {        = (Subject) Subject;        System.out.println (Sub.getdata ());}    }

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(5) User Class test class

 Public class Client {    publicstaticvoid  main (string[] args) {        new Subject ();         New Observer ();         New Observer ();        Subject.register (one);        Subject.register (both);        Subject.setdata ("Hello World");        Subject.notifyobservers ();    }}

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Design pattern Start--viewer mode