/**
 * Concrete strategy to compute the area of a circular shape: knows its own radius
 * and how to compute its area.

 * @author Dung X. Nguyen
 * <p>
 * Copyright 1999 by Dung X. Nguyen - Al rights reserved.
 */
public class Circle extends AShape
{
   private double _dRadius;

	/**
	 * Initializes this <code>Circle</code> with a given radius.

    * @param dRadius the radius, >= 0.
    * @exception IllegalArgumentException if param < 0.
	 */
	public Circle(double dRadius)
	{
      if (dRadius < 0)
      {
         throw new IllegalArgumentException ("Circle.Circle (radius): radius < 0");
      }
      _dRadius = dRadius;
	}

   /**
   *  @returns this <code>Circle</code>'s area.
   */
   public double dArea ()
   {
      return Math.PI * _dRadius * _dRadius;
   }

   /**
   * @returns a String describing a Circle and its radius.
   */
   public String toString ()
   {
      return "Circle (radius = " + _dRadius + ")";
   }
}