Java Exception Handling - Do while Loop

Question

I'm writing a Java Exception Handling program and encountered following issue.

when I enter a invalid input an infinite loop started executing instead of execution start from the try block.

public class Exception_Handling {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Scanner sc=new Scanner(System.in);
        boolean bl=true;
        do {

        try {
            int a = sc.nextInt();
            int b = sc.nextInt();
            bl=false;
        }
        catch(InputMismatchException ex) {
            System.out.println("Enter Valid Number Format");
            System.out.println(ex);
        }
        }while(bl);
    }   
}

Possible duplicate of Scanner Exception Retry

Timothy Truckle
– Timothy Truckle

2018-01-11 14:17:22 +00:00
Commented Jan 11, 2018 at 14:17 — Timothy Truckle
– Timothy Truckle, Commented Jan 11, 2018 at 14:17

Kruschenstein · Accepted Answer · 2019-06-07 15:27:04Z

3

You need to flush your buffer before re-entering in the loop. Otherwise java tries to read the same input again and again.

import java.util.Scanner;

public class Exception_Handling {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Scanner sc = new Scanner(System.in);
        boolean bl = true;
        do {

            try {
                int a = sc.nextInt();
                int b = sc.nextInt();
                bl = false;
            } catch (Exception ex) {
                System.out.println("Enter Valid Number Format");
                System.out.println(ex);
                sc.next();
            }
        } while (bl);
    }   
}

You can also use sc.reset() instead of sc.next()in your case. But if you had configured scanner with useDelimiter, useLocale or useRadix it will reset these parameters too. (see reset() java doc)

edited Jun 7, 2019 at 15:27

answered Jan 11, 2018 at 14:06

Kruschenstein

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Comments

Mohhamad Hasham · Accepted Answer · 2018-01-11 14:01:34Z

0

You have a catch exception on Input Mismatch so it won't bother to execute this statement:

bl = false;

which would not terminate the loop.

public class Exception_Handling {

public static void main(String[] args) {
    // TODO Auto-generated method stub
    Scanner sc=new Scanner(System.in);
    boolean bl=true;
    do {

    try {
        bl=false;
        int a = sc.nextInt();
        int b = sc.nextInt();

    }
    catch(InputMismatchException ex) {
        System.out.println("Enter Valid Number Format");
        System.out.println(ex);

    }
    }while(bl);
}   

}

answered Jan 11, 2018 at 14:01

Mohhamad Hasham

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