Validating string input using while loop

Question

I'm having a terribly tough time with this simple code. My while conditions are always ignored and the print statement is executed. Please help.

package Checkpoints;
import java.util.Scanner;


public class Check05 {
    public static void main (String[]args){

        Scanner keyboard = new Scanner(System.in);

        /**
         * Write an input validation that asks the user to enter 'Y', 'y', 'N', or 'n'.
         */


        String input, Y = null, N = null;

        System.out.println("Please enter the letter 'Y' or 'N'.");
        input = keyboard.nextLine();


        while (!input.equalsIgnoreCase(Y) || !(input.equals(N)))
                //|| input !=y || input !=N ||input !=n)

            {
            System.out.println("This isn't a valid entry. Please enter the letters Y or N" );
            input = keyboard.nextLine();
            }

    }

}

You are never assigning values to Y or N, and then using them in a compare. — OldProgrammer
– OldProgrammer, Commented Jul 27, 2017 at 15:43
Your Y and N are null objects. Nothing is equal to a null object. — RealSkeptic
– RealSkeptic, Commented Jul 27, 2017 at 15:43

arkantos · Accepted Answer · 2017-07-27 16:07:33Z

1

Change this;

String input, Y = null, N = null;

to this;

String input, Y = "Y", N = "N";

So that you can compare the user input string with "Y" and "N" strings.

And this;

while (!input.equalsIgnoreCase(Y) || !(input.equals(N)))

to this;

while (!(input.equalsIgnoreCase(Y) || input.equalsIgnoreCase(N)))

because your design of condition is misaimed, as @talex warned.

edited Jul 27, 2017 at 16:07

answered Jul 27, 2017 at 15:49

arkantos

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4 Comments

talex Over a year ago

Also !input.equalsIgnoreCase(Y) || !(input.equals(N)) is wrong. It should be !(input.equalsIgnoreCase(Y) || input.equalsIgnoreCase(N)).

arkantos Over a year ago

@talex Correct. Thank for the heads up pal.

talex Over a year ago

If you add it to your question it become complete, but useless because question must be deleted as off-topic anyway,

arkantos Over a year ago

Added the new condition.

lupz · Accepted Answer · 2017-07-27 15:59:43Z

0

You are comparing the input to null since you forgot to define the values of the string Y and N.

You can define the answer values in constants like so:

public static final String YES = "y";
public static final String NO  = "n";

public static void main (String[] args) {
    Scanner keyboard;
    String  input;

    keyboard = new Scanner(System.in);

    System.out.println("Please enter the letter 'Y' or 'N'.");
    input = keyboard.nextLine();

    while (!(input.equalsIgnoreCase(YES) || input.equalsIgnoreCase(NO))) {
        System.out.println("This isn't a valid entry. Please enter the letters Y or N" );
        input = keyboard.nextLine();
    }
}

EDIT: corrected the while condition as suggested by talex

edited Jul 27, 2017 at 15:59

answered Jul 27, 2017 at 15:49

lupz

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Comments

Sai G · Accepted Answer · 2019-02-24 20:00:01Z

0

Add this extra conditions before "while" loop to avoid this

    if(Y!= null && !Y.isEmpty()) 
    if(N!= null && !N.isEmpty())

edited Feb 24, 2019 at 20:00

answered Jul 27, 2017 at 15:53

Sai G

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