Calculating an area of a circle from the radius

/**
 * This works out the area of a circle A as stated in
 * Worksheet 1 exercise 1 - please see the comments
 * below to see which part of the source code answers
 * the first question. For reference, I expect that your
 * worksheet is available online through your Universities
 * online resources, but it asks to compute the area of a
 * circle as PI * Radius squared.
 *
 * @author Shaun B
 * @version 2012-10-28
 */
import java.lang.Math;
import java.util.Scanner;
public class exerciseOne
{
    // This is a constant available at a class level
    static final double PI = Math.PI;
    // This will read in our keyboard inputs via the Scanner utility
    static Scanner keyboardInput = new Scanner(System.in);
    // This will tell the main routine to continue running:
    static boolean run = true;
    public static void main(String[] args)
    {
        // Local variables available only in this scope:
        float radius = 0.00f;
        float area = 0.00f;
        int readNumber = 0;
        // Our main loop (will continue until run is set to false):
        while (run)
        {
            System.out.println("Please enter the radius of a circle");
            System.out.println("or enter 0 (zero) to exit this demonstration.");
            System.out.print("C:\\>");
            // Because we're using the scanner to read in numbers, we
            // need to try it to catch any errors:
            try
            {
                // Gets a new instance of the keyboard scanner, which takes in
                // system inputs from the keyboard, and takes the next integer
                // value
                readNumber = keyboardInput.nextInt();
            }
            // This will catch an error in case there is a problem with the
            // keyboard entry, ie, it is not an integer number or has
            // illegal characters such as alpha characters:
            catch (Exception e)
            {
                System.err.println("Illegal keyboard input in main class");
                run = false;
                // This will promptly exit the Java run-time environment:
                System.exit(0);
            }
            if(readNumber == 0)
            {
                System.out.println("Goodbye");
                run = false;
                break;
            }
            else
            {
                // This answers the criteria on the worksheet in exercise one:
                radius = readNumber;
                // Calculates the area of the circle:
                area = (float) PI * (radius * radius);
                System.out.print("The area is: ");
                // Outputs the value as a decimal number:
                System.out.format("%f\n",area);
            }
        }
        System.exit(0);
    }
}