通过值/引用传递，是什么？ [英] Pass by value/reference, what?

问题描述

该计划为6作为输出，但是当我取消对9号线，输出为5.为什么？我觉得b.a不应该改变，应该主要保持5。

  1级C1 {
2 INT 1 = 5;3公共静态无效的主要（字符串ARGS []）{
4 C1 B =新C1（）;
5 M1（B）;
6的System.out.println（b.a）;
7}8静态无效M1（C1 C）{
9 // C = C1新（）;
10 C.A = 6;
11}
12}
 

解决方案

当您在Java传递对象时，将会在由标记为B 引用意味着对象传递主方法和 C 作为参数的方法 M1 ，它们都指向同一个对象，因此，当您将值更改为6它就会体现在主方法。

当你尝试做

现在 C =新C1（）; 然后你做 C 来指向一个不同的对象，但 b 仍然指向你在你的主方法创建的对象，因此更新值6不可见的主要方法，你会得到5。

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 }

解决方案

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.

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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