Method Should Return A Double That Is Diameter Of Circle

What's that diameter? Create a new method for the circle class called diameter. Add this method to the circle class described on page 15-1. It should return a double that is the diameter of the circle. No parameters are passed to this method.

In a tester class, test the performance of your new diameter method as follows:

(Your project should have two classes, Tester and Circle.)

here is what i have so far:

public class Circle
{
public Circle (double r)
{
radius = r;
}
public double area()
{
double a = Math.PI * radius * radius;

[Code] ....