Java的this关键字在继承时的作用

class A{
    int a = 10;
    public void play(){
        System.out.println(this.a);
    }
}
class B extends A{
    private int  a = 100;
 /*   public void play(){
        System.out.println(this.a);
        System.out.println(super.a);
    }*/
}
public class test{
    public static void main(String [] args){
        A a = new B();
        a.play();
    }
}

class A{
    int a = 10;
    public void play(){
        System.out.println(this.a);
    }
    public void fun(){
        this.play();
    }
}
class B extends A{
    private int  a = 100;
    public void play(){
        System.out.println(this.a);
    }
}
public class test{
    public static void main(String [] args){
        A a = new B();
        a.play();
    }
}