問題描述

我希望有人可以為我澄清這里發生的事情.我在整數類中研究了一會兒，但因為整數 覆蓋 + 運算符我無法弄清楚出了什么問題.我的問題在于這一行:

整數 i = 0;我 = 我 + 1;//← 我認為這是在以某種方式創建一個新對象！

這是我的推理:我知道 java 是按值傳遞的(或按引用值傳遞)，所以我認為在以下示例中，整數對象應每次遞增.

公共類 PassByReference {公共靜態整數公司(整數 i){我=我+1；//我認為這一定是**偷偷**創建一個新整數...System.out.println("公司:"+i);返回我；}公共靜態無效主要(字符串[]參數){整數整數 = 新整數(0)；for (int i =0; i<10; i++){公司(整數)；System.out.println("main:"+integer);}}}

這是我的預期輸出:

這是實際輸出.

為什么會這樣?

有兩個問題:

1. 整數是按值傳遞，而不是按引用傳遞.更改方法內的引用不會反映到調用方法中傳入的引用中.
2. 整數是不可變的.沒有像 Integer#set(i) 這樣的方法.否則，您可以直接使用它.

要讓它工作，你需要重新分配 inc() 方法的返回值.

integer = inc(integer);

<小時>

要了解有關按值傳遞的更多信息，這里有另一個示例:

public static void main(String...args) {字符串[] 字符串 = 新字符串 [] { "foo", "bar" };更改參考(字符串)；System.out.println(Arrays.toString(strings));//仍然是 [foo, bar]更改值(字符串)；System.out.println(Arrays.toString(strings));//[foo, foo]}公共靜態無效changeReference(字符串[]字符串){字符串 = 新字符串 [] { "foo", "foo" };}公共靜態無效changeValue(字符串[]字符串){字符串[1] = "foo";}

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!

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);
        }
    }
}

This is my expected output:

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

This is the actual output.

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

Why is it behaving like this?

There are two problems:

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.

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

integer = inc(integer);

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";
}

這篇關于如何通過引用正確傳遞 Integer 類?的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！