Question

我正在尝试为程序中的错误输入创建一些输入验证。

该程序应该将用户输入读取为double，但如果用户键入字母而不是数字，则必须显示输入不是数字的消息。

为此，我使用带有if语句的input.hasNextDouble。 else，打印x不是数字的消息。但是，我的问题在于用户输入的第二个数字。假设用户输入“5 f”hasNextDouble解释double，然后执行if语句下的代码，但由于“f”，输入仍然不正确。

简而言之，我需要一种方法让第一个输入（5）从缓冲区中删除，这样就可以解释第二个输入。

任何帮助表示赞赏！

这是一些示例代码：

if ( keyboard.hasNextDouble() ) {


                    double i = keyboard.nextDouble();
                    double j = keyboard.nextDouble();
                    double answer = (j+i );
                    System.out.println(answer);

            }


                else  {
                    String a = keyboard.next();
                    String b = keyboard.next(); 
                    System.out.println( a + "is not a number");

Answer 1

double i,j, answer;
try{
     i = keyboard.nextDouble();
     j = keyboard.nextDouble(); 
     answer = i+j;
} catch( InputMismatchException e ) {
    // One of the inputs was not a double
    System.out.println("Incorrect format");
}

否则如果你绝对需要打印出不正确的内容，我会做if-then然后你有两次。

double i=null, j=null, answer;
// get input for i
if ( keyboard.hasNextDouble() ) {
        i = keyboard.nextDouble();
}else{
        System.out.println( keyboard.next() + " is not a double");
}
// get input for j
if ( keyboard.hasNextDouble() ) {
        j = keyboard.nextDouble();
}else{
        System.out.println( keyboard.next() + " is not a double");
}
// if both i and j received inputs             
if( i != null && j != null )
       answer = i + j;
else
       System.out.println("Malformed input");

Answer 2

你需要像以下一样。

double tryReadDouble(Scanner keyboard) throws NumberFormatException {
    if (keyboard.hasNextDouble()) {
        return keyboard.nextDouble();
    } else {
        throw new NumberFormatException(keyboard.next());
    }
}

和

try {
    double i = tryReadDouble(keyboard);
    double j = tryReadDouble(keyboard);
    double answer = (j + i);
    System.out.println(answer);
} catch (NumberFormatException ex) {
    System.out.println(ex.getMessage() + "is not a number");
}

希望这有帮助。

Answer 3

您可以创建帮助方法，该方法将询问用户有效输入，直到获得有效输入，或者直到超过某些尝试限制。这种方法可能如下所示：

public static double getDouble(Scanner sc, int maxTries) {
    int counter = maxTries;
    while (counter-- > 0) {// you can also use `while(true)` if you 
                           // don't want to limit numbers of tries
        System.out.print("Please write number: ");
        if (sc.hasNextDouble()) {
            return sc.nextDouble();
        } else {
            String value = sc.next(); //consume invalid number
            System.out.printf(
                    "%s is not a valid number (you have %d tries left).%n",
                    value, counter);
        }
    }
    throw new NumberFormatException("Used didn't provide valid float in "
            + maxTries + " turns.");
}

然后您可以使用此方法，如

Scanner keyboard = new Scanner(System.in);

double i = getDouble(keyboard, 3);
double j = getDouble(keyboard, 3);

double answer = (j + i);
System.out.println(answer);

使用扫描仪验证多个输入

3 个答案: