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)); } }
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