// TODO - write your code below this comment.
// You need to do the following:
//
// 1.) Define an abstract class named Circle
//
// 2.) Define an instance variable for Circle
//     named radius.  This variable holds a double.
//
// 3.) Define a constructor which takes a
//     double to initialize the radius instance
//     variable with
//
// 4.) Define a getter for radius
//
// 5.) Define a setter for radius
//
// 6.) Define an ABSTRACT method named getArea.
//     Abstract methods are always instance methods.
//