Question

我通过运行这个简单的java程序获得了一个奇怪的输出。

输出为：0 4 2 -6

为什么x ++打印0，应该打印4。

import java.util.*;
import java.io.*;

public class Java1 {

    public static void main(String[] args) throws IOException {

        int x = 4;
        int y = -5;

        System.out.println(x++ + " " + func(x++, y) + " " + --y);
    }

    public static int func(int work, int y) {

        int z = work + y;

        work++;

        y++;
        System.out.print(z + " ");
        return z + work + y;

    }
}

Answer 1

好的，这是正在进行的：首先评估x++，返回4（稍后打印）并将x保留为5.然后评估x++再次，将5传递给func。然后使用func和5参数评估-5。在这里z 0（5 + (-5) = 0）然后打印出来（在println方法中main之前。func然后返回{{ 1}}（2）也会添加到字符串中。最后0 + 6 + (-4)会生成--y。现在-6方法中的println会打印其字符串（main）。

Answer 2

首先执行

func(x++, y)，因此0来自System.out.print(z + " ");中的func。

Answer 3

4 2 -6

在

之前执行

System.out.print(z + " ");

因此System.out.println(x++ + " " + func(x++, y) + " " + --y);来自0，而不是z。

Answer 4

我在评论中提到了从0到7的点流

    public static void main(String[] args) throws IOException {

        int x = 4;
        int y = -5;

        System.out.println(x++ + " " + func(x++, y) + " " + --y);
        // thus 0]4  6]2 (value returned as z) 7] localvalue of --y as -6 
    }

    //1] x++ makes x as 5 when it is passed to func()
    public static int func(int work, int y) {

        int z = work + y;
        //2] z = 5 + -5 = 0 
        work++;
        //3] work which was x as 5 is now 6
        y++;
        //4] y will be -4 now
        System.out.print(z + " ");
        return z + work + y;
        //5] z = 0 + 6 + -4 = 2 and is returned to func() caller
    }

Answer 5

import java.util.*;
import java.io.IOException;

public class Java1 
{   
    public static void main(String args[])
    {
       int x = 4;
       int y = -5; 
       System.out.println("x = "+ (x++ ) +" func = "+ (func(x++, y) ) + " y = "+ --y);
    }

    public static int func(int work, int y) 
    {

        int z = work + y;// 5+-5 = 0
        work++; //6

        y++; //-4
        System.out.print("Z = " + z + " ");//0 
        return z + work + y;  //0 + 6+-4 = 2
    }
}

输出：

Z = 0 x = 4 func = 2 y = -6

这里首先执行func（），因此变量z的值打印为0，然后x ++值打印为4.

Java println奇怪的输出

5 个答案: