10. The method of rewriting Override

Method overrides: Override: the need for inheritance, the parent class that subclasses override!

1. Method name must be the same
2. Parameter list must be the same
3. Modifiers: could be expanded, but can not be reduced: public> protected> defalut> private
4. Throws an exception: range, can be reduced, but not expand; ClassNotFoundException -> Exception

Rewriting, and methods of the parent class subclasses must be consistent; different method body!

Why do I need to rewrite?

1. The parent class functions, sub-categories do not necessarily need, or may not meet!
2. Alt+Insert：Override；

. 1  Package com.oop.demo05;
 2  
. 3  // rewriting method is overridden and independent properties 
. 4  public  class B {
 . 5      public  void Test () {
 . 6          System.out.println ( "B => Test" ) ;
 7      }
 8 }

 1 package com.oop.demo05;
 2 
 3 //继承
 4 public class A extends B {
 5 
 6     //Override 重写
 7     @Override//注解：有功能的注释！
 8     public void test() {
 9         System.out.println("A=>test()");
10     }
11 }

 1 package com.oop;
 2 
 3 import com.oop.demo05.A;
 4 import com.oop.demo05.B;
 5 
 6 public class Application {
 7 
 8     public static void main(String[] args) {
 9 
10         //方法的调用只和左边，定义的数据类型有关
11         A a = new A();
12         a.test();//A=>test
13 
14         //父类的引用指向了子类
15         B b = new A();//子类重写了父类的方法，以子类重写过后的为准！
16         b.test();//A=>test
17     }
18 }