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

问题描述

抱歉，我是Java的新手，所以这个问题可能不清楚。

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

我最近一直处理在while循环中包含try和catch语句，因为我想确保从程序的其余部分包含输入。

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.

我遇到过在前面使用感叹号（！）的问题while条件中的变量（例如while（！done））而不是using = false（例如while（done = false））改变程序的运行方式。

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，只是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！在变量意味着与var = false相同之前。

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，编译和运行程序将顺利进行：它会提示我输入一个数字，输入一个字母或很长的数字会导致它打印出异常类型并退出。输入正常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.

任何人都可以解释我之间的区别！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 。第一个指定 已完成为 false 并评估为 false ，第二个将 done 与 false 进行比较，与<$ c完全相同$ c>！done 。

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
}

然后已完成设置为 false 并且while循环中的代码没有一点都不运行。

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

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