State mode (think in Java design mode)

State mode : contains a reference to a parent class object or an interface in an object. The reference points to a subclass object, which changes the class of the subclass object through an internal method, changing the same reference call to the same method to achieve different effects.

 Public classA {PrivateB b=NewB (); voidBUILDC () {b=NewC ();} voidBuildd () {b=NewD ();} voidBuilde () {b=NewE ();}  Public Static voidMain (string[] args) {A a=NewA ();        A.b.say ();        A.BUILDC ();        A.b.say ();        A.BUILDD ();        A.b.say ();        A.builde ();    A.b.say (); }    //The results are as follows://sya:b//Sya:c//sya:d//sya:e    }classb{ Public voidsay () {System.out.println ("Sya:b"); }}classCextendsB { Public voidsay () {System.out.println ("Sya:c"); }}classDextendsB { Public voidsay () {System.out.println ("Sya:d"); }}classEextendsB { Public voidsay () {System.out.println ("Sya:e"); }}

State mode (think in Java design mode)