按值/引用传递，什么? [英] Pass by value/reference, what?

问题描述

这个程序输出 6，但是当我取消注释第 9 行时，输出是 5.为什么?我认为 b.a 不应该改变，应该保持 5 为主.

This program gives 6 as output, but when I uncomment the line 9, output is 5. Why? I think b.a shouldn't change, should remain 5 in main.

1  class C1{
2      int a=5;

3      public static void main(String args[]){
4          C1 b=new C1();
5          m1(b);
6          System.out.println(b.a);
7      }

8      static void m1(C1 c){
9          //c=new C1();
10         c.a=6;
11    }
12 }

推荐答案

当你在 Java 中传递对象时，它们作为引用传递，意思是 b 在 main 方法中引用的对象和 c 作为方法 m1 中的参数，它们都指向同一个对象，因此当您将值更改为 6 时，它会反映在 main方法.

When you pass object in Java they are passed as reference meaning object referenced by b in main method and c as argument in method m1, they both point to the same object, hence when you change the value to 6 it gets reflected in main method.

现在，当您尝试执行 c = new C1(); 时，您使 c 指向不同的对象，但 b 是仍然指向您在 main 方法中创建的对象，因此更新后的值 6 在 main 方法中不可见，您得到 5.

Now when you try to do c = new C1(); then you made c to point to a different object but b is still pointing to the object which you created in your main method hence the updated value 6 is not visible in main method and you get 5.

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