Java请求双

Question

If in my program im using scanner.NextDouble() and the user enters something that is not a double ie a char of any kind, how can i re-promt them to enter a valid double? I tried throwing an exception and catching it but all i am abel to do is tell them it was wrong, im not sure how to transfer control back to the try block. if anyone has any input it would be much appreciated!

private double requestDoubleFromUser( String prompt )
{
    /*** Local Variables ***/

    Scanner sc = new Scanner( System.in );
    double userInput = 0;

    try
    {
    /*** Get input from user ***/

    System.out.print( prompt );
    userInput = sc.nextDouble();
    }

    catch( Exception e )
    {
        System.out.println("That was not a double");
    }

    return userInput;
}

thanks

Answer 1

You could use a while loop, something like this:

double userInput = 0;
boolean done = false;
while (!done) {
    try {
        /*** Get input from user ***/
        System.out.print( prompt );
        userInput = sc.nextDouble();
        done = true;
    } catch( Exception e ) {
        System.out.println("That was not a double");
    }
}

Answer 2

You could place the call to Scanner#nextDouble in a loop and consume non numeric types by catching a InputMismatchException . Using the Double type allows the loop to keep checking for an input value.

Scanner sc = new Scanner(System.in);
Double userInput = null;

while (userInput == null) {
    try {
        System.out.print("Enter double:");
        userInput = sc.nextDouble();
    } catch (InputMismatchException e) {
        System.out.println("That was not a double: " + sc.nextLine());
    }
}