建構子,override,extends

class A{
String name = "A";
String getName(){
return name;
}

String greeting(){
return "class A";
}
}
class B extends A{
String name = "B";
String greeting(){
return "class B";
}
}

public class Test {
public static void main(String[] args){
A a = new A();
A b = new B();
System.out.println(a.greeting()+" has name "+a.getName());
System.out.println(b.greeting()+" has name "+b.getName());
}
}

A a = new A();  a為A()的建構子宣告為A物件

A b = new B();  b為B()的建構子宣告為A物件

所以會印出  

Class A has name A

Class B has name A

裡面最有問題的是  b.getName()  會印出 A吧！是因為 b是 B()的建構子，可是物件是A的所以才會印出A。