Java: How to test if an input is a double or an int

Question

I have a do while loop. Checking x is between two values. Now im supposed to be taking in an int value, but if the user types a double im getting exceptions. How do I incorparate a check in the same if statement so that if the user types a double it would print something like "x must be an int between 10 and 150:"

            do {
            x = sc.nextInt();
            if ( x < 10 || x > 150 ) {
                System.out.print("x between 10 and 150: ");
            } else {
                break;
            }

Why not just use nextDouble instead of nextInt? Then check whether the specified value is equal to its integer equivalent? Admittedly that would allow "100.000" as valid input - is that a problem? — Jon Skeet
– Jon Skeet, Commented Nov 6, 2013 at 15:27
I don't know if this is a typo, but if you want your x to be between 10 and 50, your condition is wrong. You should change it to x > 10 || x < 150 — StepTNT
– StepTNT, Commented Nov 6, 2013 at 15:39
@JonSkeet This doesn't solve his problem that the Scanner method may throw exceptions, after all, user could enter something like ^Chaha\b\b\bnot a number, you fool! — Ingo
– Ingo, Commented Nov 6, 2013 at 15:41
If the print statement is correct, the condition should actually be: x >= 10 && x <= 150 — givanse
– givanse, Commented Nov 6, 2013 at 15:41

Ingo · Accepted Answer · 2013-11-06 15:38:46Z

4

You do not need an additional check. The exception is just there so you can act accordingly in your program. After all, it doesn't really matter how exactly the input was wrong. Just catch the exception (NumberFormatException, I guess?) and upon catching it, print an error message:

while (true) try {
    // here goes your code that pretends only valid inputs can occur
    break;   // or better yet, put this in a method and return
} catch (NumberFormatException nfex) {  // or whatever is appropriate
    System.err.println("You're supposed to enter integral values.");
    // will repeat due to while above
}

answered Nov 6, 2013 at 15:38

Ingo

36.4k6 gold badges57 silver badges102 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

StepTNT · Accepted Answer · 2013-11-06 16:18:21Z

3

You can just catch the exception and handle it, using a while (true) to allow the user to re-try.

Here's my code:

Scanner sc = new Scanner(System.in);
do {
    System.out.print("\nInsert a number >>> ");
    try {
        int x = sc.nextInt();
        System.out.println("You inserted " + x);
        if (x > 10 && x < 150) {
            System.out.print("x between 10 and 150: ");
        } else {
            break;
        }
    } catch (InputMismatchException e) {
        System.out.println("x must be an int between 10 and 150");
        sc.nextLine(); //This line is really important, without it you'll have an endless loop as the sc.nextInt() would be skipped. For more infos, see this answer http://stackoverflow.com/a/8043307/1094430
    }
} while (true);

edited Nov 6, 2013 at 16:18

answered Nov 6, 2013 at 15:46

StepTNT

3,9778 gold badges46 silver badges85 bronze badges

3 Comments

Govan Over a year ago

yep. The best one. +1

nachokk Over a year ago

a do while never is the best solution, besides that x between 10 and 150 should be x> 10 && x < 150

StepTNT Over a year ago

I never use the do-while but the OP used it and I didn't want to change his code. Thanks for the advice on the and, I forgot to change it when I fixed his inital condition.

givanse · Accepted Answer · 2013-11-06 15:52:14Z

0

public class SomeClass {                                                         
    public static void main(String args[]) {                                     
        double x = 150.999; // 1
        /* int x = (int) 150.999; */ // 2                                          
        if ( x >= 10 && x <= 150 ) { // The comparison will still work                                             
            System.out.print("x between 10 and 150: " + x + "\n");               
        }                                                                        
    }                                                                            
}

Declare x as double, comparisons between double and int will still work.
Or, cast the number and any decimal values will be discarded.

edited Nov 6, 2013 at 15:52

answered Nov 6, 2013 at 15:44

givanse

15k9 gold badges55 silver badges77 bronze badges

Collectives™ on Stack Overflow

Java: How to test if an input is a double or an int

3 Answers 3

Comments

3 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related