Trying to validate user input in java

Question

Sorry guys, first time poster here, so please let me know if there's some etiquette or anything I should be following!

I've seen a few of these on the forums, and I've scoured through them, trying to make one work, but I can't seem to do it.

I need to create a program that asks for the user to input two positive integers. Each time an integer is answered, I want to validate to make sure it is 1) a number and 2) also positive. If it is not, I am supposed to just terminate the program. So far, I've tried:

import java.util.Scanner;

public class Assignment4 {

    public static void main (String [] args)
    {
        Scanner in = new Scanner(System.in);
        System.out.println("Please enter two positive integers.");
        System.out.println("Please enter the first integer:");
        int num1 = in.nextInt();
    do {
        System.out.println("Invalid. ***End of Program***");
        System.exit(0);
        while (!in.hasNextInt()) {
            System.out.println("Invalid. ***End of Program***");
            System.exit(0);
                    }
        }while (num1 <= 0);
        }
    }
}

which works for when I enter a negative number, but for some reason, java just receives the invalid error input and doesn't run when I type in a letter. I also tried:

import java.util.Scanner;

public class Assignment4 {

    public static void main (String [] args)
    {
        Scanner in = new Scanner(System.in);
        System.out.println("Please enter two positive integers.");
        System.out.println("Please enter the first integer:");
        int num1 = in.nextInt()
        if (!in.hasNextInt()){
            System.out.println("Invalid integer. ***End of Program***");
            System.exit(0);
        }else if (num1 <= 0){
            System.out.println("Invalid negative number. ***End of Program***");
            System.exit(0);
}
}
}

which just doesn't do anything. I've been at this problem for about 2 hours yesterday and another hour today, looking online for other solutions. I cannot use any match or try/catch statements, as I have not learned them yet! Any insight would be great, as I'm going crazy here.

Rafael Collado · Accepted Answer · 2014-10-03 02:46:06Z

The problem here is that you're attempting to read in whatever the user inputs as an int value.

If the input happens to be something other than an integer, the program will return an InputMismatchException.

To handle this we would do the following:

int num1, num2 = 0;

try {
    System.out.println("Please enter two positive integers.");
    System.out.println("Please enter the first integer:");
    num1 = in.nextInt();

    if(num1 < 0) {
        System.out.println("Invalid integer. ***End of Program***");
        System.exit(0);

    } else {
        System.out.println("Please enter the second integer:");
        num2 = in.nextInt();

        if(num2 < 0) {
            System.out.println("Invalid integer. ***End of Program***");
            System.exit(0);
        }
} catch(InputMismatchException e) {
    System.out.println("That is not an integer. ***End of Program***");
    System.exit(0);
}
...

Hope this helps!

Juned Ahsan · Accepted Answer · 2014-10-03 02:25:32Z

1

Make use of InputMismatchException when capturing an integer using nextInt().

    int num1 = 0;
    try {
       num1 = in.nextInt()
       if(num1 < 0) {
         System.out.println(num1 + " is not a positive integer");
       }
    } catch(InputMismatchException ime) {
        System.out.println(num1 + " is not a valid integer");
    }

edited Oct 3, 2014 at 2:25

answered Oct 3, 2014 at 2:20

Juned Ahsan

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Comments

Moni · Accepted Answer · 2014-10-03 02:27:29Z

0

At the time of typing letter you are getting error because you read the text by using in.nextInt().

Try to place your code under try/catch block-

try{
     int num1 = in.nextInt();
     if (!in.hasNextInt())
     {
         System.out.println("Invalid integer. ***End of Program***");
         System.exit(0);
     }else if (num1 <= 0){
         System.out.println("Invalid negative number. ***End of Program***");
         System.exit(0);
     }
    }
    catch(InputMismatchException ime) {
         System.out.println(" not a valid integer");
    }

answered Oct 3, 2014 at 2:27

Moni

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