通过值/引用传递,什么? [英] Pass by value/reference, what?
问题描述
这个程序给出了 6 作为输出,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,应该在 main 中保持 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 }
推荐答案
当你在 Java 中传递对象时,它们作为引用的含义对象传递,由 main
方法中的 b
引用和 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
中方法.
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.
现在当你尝试做 c = new C1();
然后你让 c
指向一个不同的对象但是 b
是仍然指向您在 main
方法中创建的对象,因此更新的值 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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