Subclasses - Multimedia Introduction to Programming Using Java - page 158

Subclass Parallelogram
We design the class for the first shape, class Parallelogram . This class is
a subclass of class Shape , which provides the position of the parallelogram.
We determine what is needed to define a parallelogram whose bounding rec-
tangle has upper-left corner (x, y) . A parallelogram has two horizontal sides of
length l1 (say) and two vertical sides of length l2 (say). But this does not define
how much the parallelogram leans. For this purpose, we use a value d , which we
call the leaning factor of the parallelogram. If d is at least 0 , the parallelogram is
as defined by the diagram on the left in Fig. 4.10, and if d is negative, it is as
defined by the diagram on the right. Coordinates (x, y ), lengths l1 and l2 , and
leaning factor d completely determine the position, size, and shape of the paral-
lelogram.
We develop specs of the methods in class Parallelogram . See Fig. 4.11.
The constructor has as its parameters the five properties that define a parallelo-
gram. The class has procedure drawShape , which draws the parallelogram using
a Graphics object g . This procedure overrides drawShape in superclass Shape .
This ends the design of class Parallelogram .

Activity
4-4.2

(x,y) (x, y)

d l1 l1

l2 l2

-d

Figure 4.10: Defining a parallelogram in terms of x , y , l1 , l2 , and leaning factor d

import java.awt.*;
/** A parallelogram that can be drawn. */
public class Parallelogram extends Shape {
/** Constructor: a parallelogram with horizontal length l1 , other length l2 , bounding
box with top-left corner (x, y) , and leaning factor d

*/
public Parallelogram( int x, int y, int l1, int l2, int d) { }
/** Draw this parallelogram using g */
public void drawShape(Graphics g) { }
/** = a description of this parallelogram */
public String toString()
{ return ""; }

}

Figure 4.11: Specification of class Parallelogram