从超类访问阴影变量

Question

From this anwser , he said that we can access shadowed variables from superclasses of superclasses by casting this , but it doesn't work for method calls because method calls are determined based on the runtime type of the object.

However, why can I still get shadowed variables without explicitly casting the passing parameter types?

interface I { int x = 0; }
class T1 implements I { int x = 1; }
class T2 extends T1 implements I { int x = 2; }
class T3 extends T2 implements I {
    int x = 3;

    void test() {
        System.out.println("((T3)this).x=" + ((T3)this).x + "; getT3(this)=" + getT3(this));
        System.out.println("((T2)this).x=" + ((T2)this).x + "; getT2(this)=" + getT2(this));
        System.out.println("((T1)this).x=" + ((T1)this).x + "; getT2(this)=" + getT1(this));
        System.out.println("((I)this).x=" + ((I)this).x + "; getI(this)=" + getI(this));
    }

    public static void main(String[] args) {
        new T3().test();
    }

    int getT3(T3 t3) { return t3.x; }
    int getT2(T2 t2) { return t2.x; }
    int getT1(T1 t1) { return t1.x; }
    int getI(I i) { return i.x; }
}

which produces the output:

((T3) this).x = 3; getT3(this) = 3
((T2) this).x = 2; getT2(this) = 2
((T1) this).x = 1; getT1(this) = 1
((I) this).x = 0; getI(this) = 0

If I understand his anwser correctly, shouldn't getT3 , getT2 , getT1 and getI methods all return 3?

Answer 1

Because the method signatures expect I , T1 , T2 , and T3 , the parameters are treated as those types when returning ix , t1.x , etc.

So calling getT2(this) is essentially equivalent to calling getT2((T2) this) .

That's why they would not all return 3, but rather the value of x for that specific type.

I'm not sure I've explained this well, but because T3 extends T2 , it is implicitly cast to an instance of T2 when passed to getT2 .