Java中的循环问题

while (boolean always = true) {
    } // DOES NOT COMPILE!!!

你必须在循环之前和之外声明变量,所以可能是这样的：

boolean always = true;
    while (always) {
        break;
    } // compiles fine!

    // always is still in scope after the loop!
    always = !always;

从这个意义上讲,for循环是唯一的：事实上你可以声明一个新的局部变量,其范围仅限于该循环：

for (boolean always = true; always; ) {
        break;
    } // compiles fine!

    // always is no longer declared after the loop!
    always = !always; // DOES NOT COMPILE!

也就是说,看看你在做什么,你可能想看看java.util.Scanner.我怀疑它会更好地满足你的需求.

例

下面是使用Scanner从标准输入读取数字的示例,终止于0.然后打印这些数字的总和.它使用hasNextInt()而不是Integer.parseInt/NumberFormatException正常处理无效输入.

Scanner sc = new Scanner(System.in);
    System.out.println("Enter numbers (0 to end):");
    int sum = 0;
    int number;
    do {
        while (!sc.hasNextInt()) {
            System.out.println("I'm sorry,that's not a number! Try again!");
            sc.next();
        }
        number = sc.nextInt();
        sum += number;
    } while (number != 0);
    System.out.println("The sum of those numbers is " + sum);

这是一个示例会话：

Enter numbers (0 to end):
1
3
-1
five
I'm sorry,that's not a number! Try again!
2
0
The sum of those numbers is 5