Question

我在验证方面遇到了一些麻烦。这是我的代码

    int a = keyboard.nextInt();
    int b = keyboard.nextInt();
    while(x < -50 || x > 50 && y < -50 || y > 50)
    {
        System.out.println("Error " + a + " is out of range");
        System.out.println("Error " + b + " is out of range");
        System.out.println();
        System.out.print("Input two integers in the range [-50, + 50]: ");
        a = keyboard.nextInt();
        b = keyboard.nextInt();
    }
    while( x < -50 || x > 50)
    {
        System.out.println("Error " + a + " is out of range");
        System.out.println();
        System.out.print("Input two integers in the range [-50, + 50]: ");
        a = keyboard.nextInt();
        b = keyboard.nextInt();
    }
    while( y < -50 || y > 50)
    {
        System.out.println("Error " + b + " is out of range");
        System.out.println();
        System.out.print("Input two integers in the range [-50, + 50]: ");
        a = keyboard.nextInt();
        b = keyboard.nextInt();
    }

我的问题是，用户输入需要是＆amp; b来自[-50,50]

但是当我输入-100和100时，我只得到a超出范围或b超出范围而不是两者。

Input: a= -100 b = 100
Output: 
System.out.println("Error " + -100 + " is out of range"); // CORRECT
System.out.println("Error " + 23 + " is out of range"); // ? INCORRECT

我做错了什么

Answer 1

使用绝对值，请记住 |a| < x means -x < a < x 因此 a 和 b 必须符合条件或其他方式，只要**a > 50**或**b > 50**

，您就会问

int a = -100;
int b = -100;
Scanner scan = new Scanner(System.in);
while (Math.abs(a) > 50 || Math.abs(b) > 50) {
    System.out.println("need a:");
    a = scan.nextInt();
    System.out.println("need b:");
    b = scan.nextInt();
}
scan.close();
System.out.println("am gone!");

Answer 2

检查while循环。
while( x <= -50 || x >= 50 && y <= -50 || y > 50)

两个条件都必须为true才能成功执行。检查&&

Answer 3

你对运营商的优先权感到顽皮。

x <= -50 || x >= 50 && y <= -50 || y > 50

评估为

x <= -50 || (x >= 50 && y <= -50) || y > 50

你需要加上一些括号：

(x <= -50 || x >= 50) && (y <= -50 || y > 50)

另外，请检查a，b，x和y之间的确切关系。为什么要分配到a和b，然后立即测试x和y？

Answer 4

正如评论中所解释的那样，您正在测试x和y，但是阅读a和b。

此外，您的代码可以简化：

boolean valid = true;
do {

    System.out.print("Input two integers in the range [-50, + 50]: ");
    int a = keyboard.nextInt();
    int b = keyboard.nextInt();

    if ( (a < -50) || (a > 50) ) {
        valid = false;
        System.out.println("Error " + a + " is out of range");
    }

    if ( (b < -50) || (b > 50) ) {
        valid = false;
        System.out.println("Error " + b + " is out of range");
    }

} while (!valid);

Answer 5

while( x <= -50 || x >= 50 && y <= -50 || y > 50) Java使用逻辑运算符的“短路评估”。因此，如果x = -100且y = 0，则将输入循环，因为-100 <= -50且没有其他条件，因为true || anything始终为真。使用括号控制逻辑操作的处理方式。我建议将控制while循环的布尔条件放入一个名称很好的方法中。

private boolean bothParamsAreOutOfRange(int x, int y) {
    boolean rtn = false;
    if ((x <= -50 || x >= 50) && (y <= -50 || y > 50)) {
       rtn = true;
    }
    return rtn;
}

while(bothParamsAreOutOfRange(x, y)) {
    ... as before ...
}

使用while循环验证时出错

5 个答案: