java - 按引用调用或按值调用

Question

有人可以解释一下这个程序是如何执行的吗？

这是我似乎不太明白其输出的代码:

    class Box {
        int size;
        Box (int s) {
           size = s;
        }
    }
    public class Laser {
        public static void main(String[] args) {
            Box b1 = new Box(5);
            Box[] ba = go(b1, new Box(6));
            ba[0] = b1;
            for(Box b : ba)
                System.out.println(b.size + " ");
        }

        static Box[] go (Box b1, Box b2) {
            b1.size = 4;
            Box[] ma = {b2, b1};
            return ma;
        }
    }

我运行时的实际输出是 4, 4。但根据我的理解，这应该是 5, 4。 任何人都可以帮助理解这是如何执行的吗？

Answer 1

我已经为你添加了评论；

The important TWIST that you missed here is;

Box[] ma = {b2, b1}; 它不是 {b1,b2}。返回时内存位置会互换。

       public static void main(String[] args) {
            Box b1 = new Box(5);                 // b1 == location A
            Box[] ba = go(b1, new Box(6));       // ba == location B which stores Location A, D

           // PLEASE NOTE HERE
           // After the function go() is executed;
           // ba[] will have {D, A}
           // So ba[0] will have object b1 which is at location A. 

            ba[0] = b1;                          // location B will now store A and A
            for(Box b : ba)
                System.out.println(b.size + " ");  //  Output: 4 and 4
        } 

        static Box[] go (Box b1, Box b2) {        // go(location A, location D )
            b1.size = 4;                          // A's object.size = 4
            Box[] ma = {b2, b1};                  // position is interchanged here (D and A)
            return ma;                            // return the location of ma
        }

希望这有帮助。

如果您有任何疑问，请告诉我。 java中一切都是按值传递的。内存地址按值传递。