Question

我是Java的新手。我希望代码在用户输入错误类型的位置重复，而不是从头开始。当在“输入b：”或“输入c：”时，它会回到开头“输入：”。我希望它只重复，用户输入是a，b，c。提前谢谢。

public static void main(String[] args)
{
Scanner sc = new Scanner(System.in);
boolean itsANumber = true;
while (itsANumber)
{
    System.out.print("Enter a: ");

    try
    {
    a = Double.parseDouble(sc.nextLine());

    System.out.print("Enter b: ");
    try
    {
        b = Double.parseDouble(sc.nextLine());

        System.out.print("Enter c: ");
        try
        {
        c = Double.parseDouble(sc.nextLine());
        if (a == 0)
        {
            aZero();
        } else

        {
            aNotZero();
        }

        } catch (NumberFormatException nfe) 
        {
        System.out
            .println("That's not a number, please try again!");
        }

    } catch (NumberFormatException nfe) 
    {
        System.out
            .println("That's not a number, please try again!");
    }

    } catch (NumberFormatException nfe) 
    {
    System.out.println("That's not a number, please try again!");
    }
}

}

Answer 1

介绍一个要求输入数字的方法并将其调用三次。在方法内，您将while循环try-catch。

public static void main(String... args) {
   Scanner sc = new Scanner(System.in);
   double
     a = askForDouble(sc, "a"),
     b = askForDouble(sc, "b"),
     c = askForDouble(sc, "c");
}
static double askForDouble(Scanner sc, String varName) {
   for (;/*ever*/;) {
     System.out.format("Enter %s: ", varName);
     System.out.flush();
     try {
       return Double.parseDouble(sc.nextLine());
     } catch (NumberFormatExcetpion() {
       System.out.println("That's not a number, please try again!");
     }
   }
}

Answer 2

您可以尝试通过简单的空值检查，如果您需要，如下所示，这是原始代码，可能需要更改

Double a = null;
Double b = null;
Double c = null;
Scanner sc = new Scanner(System.in);
while(true){

    if(a != null){              
        System.out.println("Enter a :");
        a = readFromInStream(sc, "a");
            if(a == null) continue;
    }
    if(b != null){              
        System.out.println("Enter b :");
        b = readFromInStream(sc, "b");
            if(b == null) continue;
    }
    if(c != null){              
        System.out.println("Enter c :");
        c = readFromInStream(sc, "c");
            if(c == null) continue;
    }
    if(a != null && b != null && c != null){
        break;
    }
}

private Double readFromInStream(Scanner sc, String varStr){
    Double temp = null;
    try
    {
        temp = Double.parseDouble(sc.nextLine());
    }catch(NumberFormatException e){
        System.out.println("Invalid value for :"+varStr);
    }
    return temp;
}

虽然真的尝试抓住嵌套

2 个答案: