Problem

Prompt the user for input until they enter either a, b, or c. Use the following guidelines in coming up with a solution:

• [JOptionPane for input]
• While loop for validating input

While and For Loops

Solution

To use JOptionPane you will need to include the following import statement.

import javax.swing.JOptionPane; //needed for JOptionPane

We will need one String variable message. For getting input from the JOptionPane input dialog.

String message; //used to store the input from the user.

To get input from the user we use the following line of code.

//gets input from the user
message = JOptionPane.showInputDialog("Please Enter a, b or c:");

To validate our input we are going to need to used the .equals() method. For strings this will compare the contents of two passed strings. The equals method returns true if the two strings matched.

//checks if message is equal to a
//returns true if true
message.equals("a")

For our problem we want to continue to ask until we get a valid letter. While loops keep running while the test condition = true. So we have to negate the returned value so that we get false to exit the loop on valid input. We can use "!" in front of the method call to negate the answer.

boolean result;

//result will now equal false when message = "a"
result = !(message.equals("a"))

Code

Solution Code

import javax.swing.JOptionPane; //needed for JOptionPane

public class InputValidation
{
    public static void main(String [ ] args)
    {
        String message; //used to store the input from the user.

        //gets input from the user
        message = JOptionPane.showInputDialog("Please Enter a, b or c:");

        while(!message.equals("a") && !message.equals("b") && !message.equals("c"))
        {
            //gets input from the user
            message = JOptionPane.showInputDialog("Please Enter a, b or c:");
        }
    }
}