/*
   Circle is a class representing the mathematical concept of circle.  
   This class includes the following operations: 
   <ul>
     <li>Increase the size</li>
     <li>Decrease the size</li>
     <li>Report the circumference</li>
   </ul>
   <p>
   This class is written for the Java tutorials of SE2AA4 (Winter 07).
  
   @author Clare So
  
  */
public class Circle {

   private double diameter;  // The diameter of the circle

   /**
      The diameter of the circle is 10cm by default.
     */
   public Circle() {
      diameter = 10.0;
   }

   /**
      The circle can be initialized of other sizes.
     
      @param d diameter of the new circle
     */
   public Circle(double d) {
      diameter = d;
   }

   /**
      Make the circle bigger 
     
      @param factor Centimetres to be added to the diameter
      @return updated diameter 
     */
   public double grow(double factor) {
      diameter = diameter + factor;
      return diameter;
   }

   /**
      Make the circle smaller
     
      @param factor Centimetres to be subtracted from the diameter
      @return updated diameter 
     */
   public double shrink(double factor) {
      diameter = diameter - factor;
      return diameter;
   }

   /**
      Return the diameter of the circle 
     
      @return current diameter 
     */
   public double getDiameter() {
      return diameter;
   }

   /**
      Calculate the circumference of the circle
     
      @return circumference of the circle 
     */
   public double calculatetCircumference() {
      double PI = 3.14;
      return diameter*PI;
   }

   /**
      Report the diameter of the circle by a string
     
      @return a sentence reporting the diameter of the circle 
     */
   public String toString() {
      return "The diameter of this circle is " + diameter + " cm.";
   }
}