/**
 * Concrete strategy to compute the area of a rectangular shape: knows its own width
 * and height and how to compute its area.

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

	/**
	 * Initializes this <code>Rectangle</code> width a given width and a given height

    * @param dWidth width of this <code>Rectangle</code>, >= 0.
	 * @param dHeight height of this <code>Rectangle</code>, >= 0.
    * @exception IllegalArgumentException, if params do not satisfy preconditions.
	 */
	public Rectangle(double dWidth, double dHeight)
	{
      if (dWidth < 0 || dHeight < 0)
      {
         throw new IllegalArgumentException ("Rectangle.Rectangle (width, height): width < 0) or height <0.");
      }
      _dHeight  = dHeight;
      _dWidth   = dWidth;
	}

   /**
   *  @returns this <code>Rectangle</code>'s area.
   */
   public double dArea()
   {
      return _dHeight * _dWidth;
   }

   /**
   * @returns a String describing a Rectangle with its width and height.
   */
   public String toString ()
   {
      return "Rectangle (width = " + _dWidth + ", heigth = " + _dHeight + ")";
   }
}