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2.3 A Rect Subclass
Example 2-3 is a simple
subclass of the Rect class of Example 2-1. This DrawableRect class
inherits the fields and methods of Rect and adds
its own method, draw( ), that draws a rectangle
using a specified java.awt.Graphics object.
(We'll see more of the Graphics
object in Chapter 12.)
DrawableRect also defines a constructor that
simply uses the super keyword to pass its
arguments up to the corresponding Rect
constructor. Note the use of the extends keyword
to indicate that Rect is the superclass of
DrawableRect.
Example 2-3. DrawableRect.java
package je3.classes;
/**
* This is a subclass of Rect that allows itself to be drawn on a screen.
* It inherits all the fields and methods of Rect
* It relies on the java.awt.Graphics object to perform the drawing.
**/
public class DrawableRect extends Rect {
/** The DrawableRect constructor just invokes the Rect( )
constructor */
public DrawableRect(int x1, int y1, int x2, int y2)
{ super(x1,y1,x2,y2); }
/** This is the new method defined by DrawableRect */
public void draw(java.awt.Graphics g) {
g.drawRect(x1, y1, (x2 - x1), (y2-y1));
}
}
