如何通过引用正确传递Integer类？ [英] How can I pass an Integer class correctly by reference?

问题描述

我希望有人可以为我澄清这里发生的事情。我在整数类中挖了一下但因为整数覆盖 + 运算符我无法弄清楚出了什么问题。我的问题在于这一行：

I am hoping that someone can clarify what is happening here for me. I dug around in the integer class for a bit but because integer is overriding the + operator I could not figure out what was going wrong. My problem is with this line:

Integer i = 0;
i = i + 1;  // ← I think that this is somehow creating a new object!

这是我的理由：
我知道java是按值传递的（或传递引用值），所以我认为在下面的示例中，整数对象应该每个都递增时间。

Here is my reasoning: I know that java is pass by value (or pass by value of reference), so I think that in the following example the integer object should be incremented each time.

public class PassByReference {

    public static Integer inc(Integer i) {
        i = i+1;    // I think that this must be **sneakally** creating a new integer...  
        System.out.println("Inc: "+i);
        return i;
    }

    public static void main(String[] args) {
        Integer integer = new Integer(0);
        for (int i =0; i<10; i++){
            inc(integer);
            System.out.println("main: "+integer);
        }
    }
}

这是我的预期输出：

Inc: 1
main: 1
Inc: 2
main: 2
Inc: 3
main: 3
Inc: 4
main: 4
Inc: 5
main: 5
Inc: 6
main: 6
...

这是实际输出。

Inc: 1
main: 0
Inc: 1
main: 0
Inc: 1
main: 0
...

为什么它会像这样？

推荐答案

有两个问题：

1. 整数是按值传递的，而不是通过引用传递的。更改方法内部的引用将不会反映到调用方法中的传入引用中。


2. 整数是不可变的。没有像整数#set（i）这样的方法。否则你可以使用它。

1. Integer is pass by value, not by reference. Changing the reference inside a method won't be reflected into the passed-in reference in the calling method.
2. Integer is immutable. There's no such method like Integer#set(i). You could otherwise just make use of it.

要使它工作，你需要重新分配<$ c的返回值$ c> inc（） method。

To get it to work, you need to reassign the return value of the inc() method.

integer = inc(integer);

---

要了解更多关于按值传递的信息，这是另一个例子：

---

To learn a bit more about passing by value, here's another example:

public static void main(String... args) {
    String[] strings = new String[] { "foo", "bar" };
    changeReference(strings);
    System.out.println(Arrays.toString(strings)); // still [foo, bar]
    changeValue(strings);
    System.out.println(Arrays.toString(strings)); // [foo, foo]
}
public static void changeReference(String[] strings) {
    strings = new String[] { "foo", "foo" };
}
public static void changeValue(String[] strings) {
    strings[1] = "foo";
}

这篇关于如何通过引用正确传递Integer类？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！