CODEWITHSUNDEEP
javavalidationwhile-loop
Brittany Gefroh
Brittany Gefroh

Reputation: 81

Having problems with hasNextDouble method in Java

In my program, I have the user input a radius value and then the program outputs the area and perimeter.

I want to make sure the user types in a number, so I used the hasNextDouble() method. It's not quite working correctly, though.

When the program runs the first while loop that I bolded (apparently, I can't bold code, so it's the code with asterisks surrounding it) in my code below, the words "Please enter a number > " appear as intended.

However, if the program runs the second while loop that I bolded (which is nested inside a while loop that tests if the number from the user is positive), "Please enter a number > " appears twice.

I can't figure out why those words are printing twice. Can anyone help?

/**
 * Uses the Circle class to calculate area and perimeter of a circle based on a user-provided radius.
 * 
 * @author Brittany Gefroh
 * @version 1.0
 */

//Import the Scanner class
import java.util.Scanner;

public class CircleTest
{
public static void main (String [] args)
{
    //Initialize a Scanner object
    Scanner scan = new Scanner(System.in);

    //Create new Circle object
    Circle circle1 = new Circle();

    //Declare variables
    double input;
    String garbage;
    String answer;

    //Do/while loop answer is Y or y
    do
    {
        //Ask user for a radius value
        System.out.print("Enter a radius value > ");

        **while ( ! scan.hasNextDouble())
        {
            garbage = scan.nextLine();
            System.out.print("\nPlease enter a number > ");
        }**

        //Assign user input to the input variable
        input = scan.nextDouble();

        //Test if input is a positive number
        while (input <= 0)
        {
            //Prompt user for a new radius value
            System.out.println("Radius must be greater than 0");
            System.out.print("\nEnter a radius value > ");

            **while ( ! scan.hasNextDouble())
            {
                garbage = scan.nextLine();
                System.out.print("\nPlease enter a number > ");
            }**

            //Assign user input to the input variable
            input = scan.nextDouble();
        }

        //Run the setRadius method to change the radius
        circle1.setRadius(input);

        //Print blank space
        System.out.println("");

        //Display output
        System.out.println("The radius is " + circle1.getRadius());
        System.out.println("The area is " + circle1.getArea());
        System.out.println("The perimeter is " + circle1.getPerimeter());

        //Print blank space
        System.out.println("");

        //Ask user if he/she wants to try again
        System.out.print("Would you like to try again? Y or N > ");
        answer = scan.next();

        //Print blank space
        System.out.println("");

    }while (answer.equalsIgnoreCase("Y"));

}
}

Upvotes: 1

Views: 2431

Answers (1)

msi
msi

Reputation: 2639

Change:

answer = scan.next();

To:

scan.nextLine();
answer = scan.nextLine();

Maybe you should try to simplify this code by creating a specialized method for reading double with validation attached to it? Also try to think why you have these 'empty' nextLine() operations. Are these necessary?

edit...

The problem is that scan.nextDouble(); do not remove EOL marker (End Of Line). The same is with scan.next();. That is your issue. EOL marker is analized by while condition and it shows:

"Please enter a number > " <immediate EOL answer which was left in scanner>
"Please enter a number > " <now we are waiting for user input>

Upvotes: 2

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