Java Object-oriented---polymorphism

The manifestation of polymorphism

1. Overloading and rewriting of methods

2, the polymorphism of the object

The polymorphism of the object

Upward transformation

The program will automatically complete

Parent class Parent Class object = Child class instance

Down transformation

Forced type conversion ( downward transformation must first be shifted upward, then downward )

Subclass sub-Class object = (subclass) Parent class instance

Eg:a a=new b;b b= (B) A;

The use of polymorphism

A simple example:

classA { Public voidTell () {}}classBextendsA { Public voidtellb () {}}classCextendsA { Public voidTELLC () {}} Public classDemo { Public Static voidMain (String args[]) {Say (NewB ()); Say (NewC ()); } Public voidsay (a a) {A.tell (); }}

Note: If you do not use polymorphism, you need to overload the say method, and there are several object calls that need to be overloaded several times. In this case, the more redundant code is generated. The demo code is as follows:

 Public class demo{
　　 Public Static void　　　　Main (String args[]) {Say (new  B ());　　Say (new  C ());　　}  publicvoid  say (b b) {B.tell ();　　}  publicvoid  say (c c) {C.tell (); }}

instanceof Keywords

Role

Determines whether an instance is an object of a class and returns a Boolean

The sample code is as follows:

Newinstanceofinstanceof newinstanceof    instanceof B); execution Result: True false True True   

Java Object-oriented---polymorphism