为什么for语句后的分号会导致编译错误? [英] Why does a semicolon after a for statement cause a compile error?

问题描述

对于我的Java类，要求我们在工作中的for语句中添加分号，并说明输出为何如此.我不明白为什么添加分号会导致错误的树类型错误，从而导致代码无法编译.代码下面是输出；我还向任何标记添加了反斜杠，因为它没有显示其他方式.那么，为什么在for语句后的分号会导致这种错误?预先感谢.

For my Java class, we are asked to add a semicolon to a working for statement and explain why the output is what it is. I don't understand why adding the semicolon creates an erroneous tree type error resulting in the code being unable to compile. Below the code is the output; I have also added backslashes to the any tag because it wasn't displaying otherwise. So, why does a semicolon after a for statement cause such an error? Thanks in advance.

package fordemo;

import java.util.Scanner;

public class ForDemo {
    public static void main(String[] args) {
        {
            Scanner user_input = new Scanner(System.in);
            System.out.println("Input a number:");
            int number = user_input.nextInt();
            for (int n = 1; n <= number; n += 2) ;
            System.out.print(n + " ");
        }
    }
}

运行:

Input a number:

9

Exception in thread "main" java.lang.RuntimeException: Uncompilable source code - 
Erroneous tree type: <\any>\

at fordemo.ForDemo.main(ForDemo.java:35)

Java Result: 1

BUILD SUCCESSFUL (total time: 1 second)

推荐答案

您正在使用; ... for (int n = 1; n <= number; n += 2);<-终止for-loop，在这里请参见;循环不执行任何操作，然后n变为未定义，是因为它仅在for-loop本身的上下文中定义...

You're teminating the for-loop with a ;...for (int n = 1; n <= number; n += 2); <--- See ; here, this means that the loop does nothing and then n becomes undefined, is it's defined only within the context of the for-loop itself...

尝试类似...

for (int n = 1; n <= number; n+=2 ) {
    System.out.print(n + " ");
}

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