The observer pattern in Java internal implementation

If the admin wants to observe user's salary change, when the user's salary increases or decreases, will cause the admin to output the corresponding information.

Defining the Observer Interface: Myobserver.java

 Package Cn.liuning.watch;  Public Interface myobserver {    void  update (myobservable o, Object arg);}

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Define the observed parent class (the Admin class needs to inherit this class): Myobservable.java

 PackageCn.liuning.watch;ImportJava.util.Observer;ImportJava.util.Vector;/*** Viewer mode, Java source code *@authorliuning **/ Public classmyobservable {/*** Mark whether to be observed this change*/    Private BooleanChanged =false; /*** Save all the observers*/    PrivateVector<myobserver>All ; /*** Viewer Constructor*/     Publicmyobservable () { all=NewVector<myobserver>(); }        /*** Add a viewer *@paramo*/     Public synchronized voidaddobserver (Myobserver o) {if(O = =NULL){            Throw NewNullPointerException (); }        if(!all.contains (o))        {all.addelement (o); }    }        /*** Delete an observer *@paramo*/     Public synchronized voiddeleteobserver (Observer o) {all.removeelement (o); }        /*** Be observed this informs the observer to make corresponding changes*/     Public voidnotifyobservers () {notifyobservers (NULL); }        /*** Be observed this informs the observer to make corresponding changes*/     Public voidnotifyobservers (Object Arg) {object[] arrlocal; synchronized( This) {            if(!changed) {                return ; } arrlocal=All.toarray ();        Clearchanged (); }         for(inti = arrlocal.length-1; i>=0; i--) {((myobserver) arrlocal[i]). Update ( This, ARG); }     }        /*** Delete all observers*/      Public synchronized voiddeleteobservers () {all.removeallelements (); }          /*** Settings are observed this changes*/     protected synchronized voidsetchanged () {changed=true; }          /*** Clear Changes*/     protected synchronized voidclearchanged () {changed=false; }          /*** Determine if there is a change *@returnBoolean*/      Public synchronized BooleanhasChanged () {returnchanged; }          /*** Count, get the number of observers *@return      */      Public synchronized intcountobservers () {returnall.size (); }    }

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Define observer (need to implement Myobservable interface): Admin.java

 Package Cn.liuning.watch;  Public class Implements myobserver{    @Override    publicvoid  update (myobservable o, Object Arg) {                = (User) o;                System.out.println (Arg+ "money changed");                System.out.println (User.tostring ());    }    }

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Define the Observer (need to inherit Myobserver): User.java

 PackageCn.liuning.watch; Public classUserextendsmyobservable{Private intPrice = 0; PrivateString name = "Zhang San";  PublicString GetName () {returnname; }     Public voidsetName (String name) { This. Name =name; }     Public intGetPrice () {returnPrice ; } @Override PublicString toString () {return"User [price=" + Price + ", name=" + name + "]"; }     Public voidSetprice (intPrice ) {                 This. Price =Price ; //set a change in salary         This. setchanged (); //notifies the observer to execute, and internal is the call to all observers of the Update method, through the interface implementation.          This. Notifyobservers ( This. name);//Lunch can also be used as a reference    }    }

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Test the Main method: Test.java

 PackageCn.liuning.watch; Public classTest { Public Static voidMain (string[] args) {//initialized by the ObserverUser User =NewUser (); //Add an observerUser.addobserver (NewAdmin ()); User.setname ("John Doe"); //when the price changes, the viewer executes the Update method. User.setprice (100); }}

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The observer pattern in Java internal implementation