Java 中的 while (x = false) 和 while (!x) 有什么区别? [英] What is the difference between while (x = false) and while (!x) in Java?

问题描述

抱歉，我是 Java 新手，所以这个问题可能不清楚.

Sorry, I'm new to Java, so this question might be unclear.

我最近一直在处理在 while 循环中包含 try 和 catch 语句的问题，因为我想确保获取输入是从程序的其余部分中包含的.

I have been recently dealing with enclosing a try and catch statement in a while loop, because I wanted to make sure that getting input was enclosed from the rest of the program.

我遇到了一个问题，即在 while 条件(例如 while (!done))中的变量前使用感叹号 (!) 而不是使用 = false(例如 while (done = false))会改变我的程序运行的方式.

I have come across a problem where using an exclamation mark (!) in front of a variable in the while conditions (e.g. while (!done)) instead of using = false (e.g. while (done = false)) changes the way my program runs.

前者 (!done) 导致 try 和 except 语句按预期运行.后者 (done = false) 不会，只需跳过它们并转到代码的下一部分.

The former (!done) results in the try and except statements running as expected. The latter (done = false) does not, simply skipping them and moving on to the next part of the code.

我的印象是！在变量之前与 var = false 含义相同.

I was under the impression that ! before a variable meant the same thing as var = false.

我错了吗?

这是一个例子:

import java.util.Scanner;

public class TestOne {
    public static void main(String args[]) {
        Scanner input = new Scanner(System.in);
        int num;
        boolean inputDone = false;
        while (!inputDone) {
            try {
                System.out.print("Enter in a number here: ");
                num = input.nextInt();
                inputDone = true;
            }
            catch (Exception e) {
                System.out.println(e);
                System.exit(0);
            }
        }
        System.out.println("Success!");
    }
}

目前，编译和运行程序会很顺利:它会提示我输入一个数字，输入一个字母或非常长的数字会导致它打印出异常类型并退出.输入普通数字会导致打印成功！

Currently, compiling and running the program will go smoothly: it will prompt me for a number, typing in a letter or really long number causes it to print out the exception type and exit. Typing in a normal number causes it to print Success!

另一方面，如果我用 inputDone = false 替换 !inputDone，它只会打印出 Success！当我运行程序时.

On the other hand, if I were to replace !inputDone with inputDone = false, it simply prints out Success! when I run the program.

谁能给我解释一下！和 while 循环中的 = false 语句?

Can anyone explain the difference to me between the ! and the = false statements in a while loop?

推荐答案

注意 done = false 和 done == false 之间的区别.第一个 assigns done 为 false 并评估为 false，第二个比较 done 带有 false 并且与 !done 完全相同.

Note the difference between done = false and done == false. The first one assigns done to be false and evaluates as false, the second one compares done with false and is exactly identical to !done.

所以如果你使用:

while (done = false)
{
 // code here
}

然后将 done 设置为 false 并且 while 循环中的代码根本不运行.

Then done is set to false and the code within the while loop doesn't run at all.

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