java - 对接口(interface)的空引用如何返回值？

Question

代码是:

interface I {
    int i = 0;
    void display();
}

class A implements I {
    I i1;

    public static void main(String[] args) {
        A a = new A();
        a.display();
    }

    public void display() {
        System.out.println(i1); //1
        System.out.println(i1.i); //2
    }
}

代码的输出是

null
0

但是当i的地址为null时，那么在第二个i1.i中它是如何返回一个值的呢？如何使用空引用指向变量？

Answer 1

Fields declared in interfaces are implicitly static.

Every field declaration in the body of an interface is implicitly public, static, and final. It is permitted to redundantly specify any or all of these modifiers for such fields.

这个

i1.i

是一个static 字段访问表达式。它依赖于 i1 的类型，而不是它的值。它完全等同于

I.i // where I is the name of your interface