函数不会改变java中变量的值? [英] function won't change value of variable in java?

问题描述

我知道java中的一切都是按值传递的，但下面的代码不应该打印2而不是1.

I know that everything in java is passed by value but shouldn't the below code print 2 instead of 1.

我所做的只是传递 Integer 并更改其值.为什么打印 1 而不是 2 ?

All I am doing is passing Integer and changing its value. Why is it printing 1 instead of 2 ?

public static Integer x;

public static void doChange(Integer x) {
    x = 2;
}

public static void main(String arg[]) {
    x = 1;
    doChange(x);
    System.out.println(x);
}

推荐答案

非常感谢您的回答.我想我现在知道幕后发生了什么.我认为我看不到 main 函数变化的原因是整数是不可变的，当我为其分配新值时，它会创建新对象并分配给引用 x；

thank you so much for your answers. i think i know now what is happening under the hood. i think the reason i am not able to see changes in main function is because integer is immutable and when i am assigning new value to it, its creating new object and assigning to the reference x;

如果我们可以用可变数据重复相同的例子，我们会看到不同的输出.

if we can repeat same example with mutable data we ll see different output.

public static StringBuilder x;

public static void doChange(StringBuilder x)

{

    x.append("world");

}

public static void main(String arg[]) {
    x = new StringBuilder("hello ");

    doChange(x);

    System.out.println(x);
}

输出:你好世界

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