子类覆盖父类的成员变量

class A {
int a = 100;

void f() {
System.out.println(a);
}
}

class B extends A {

int a = 9999;

void f() {
System.out.println(a);
System.out.println(this.a);
System.out.println(super.a);

}

}

public class TestClient {

private static Context context;

public static void main(String[] args) {

A a = new B();
System.out.println(a.a);
a.f();
System.out.println("======================");
B b = new B();
b.f();
System.out.println("=======================");
((A) a).f();
}

}

100
9999
9999
100
======================
9999
9999
100
=======================
9999
9999
100