Discovering Classes and Objects - Beginning Java 7 - page 155

Because Point and Circle instancesaredrawablesbyvirtueoftheseclassesim-
plementingthe Drawable interface,itislegaltoassign Point and Circle instance
references to variables (including array elements) of type Drawable .
When you run this method, it generates the following output:
Point drawn at (10, 20) in color 1
Circle drawn at (10, 20) with radius 30 in color 1
Listing2-42 's Drawable interfaceisusefulfordrawingashape'soutline.Suppose
youalsoneedtofillashape'sinterior.Youmightattempttosatisfythisrequirementby
declaring Listing 2-44 's Fillable interface.

Listing 2-44. Declaring a Fillable interface

interface Fillable
{

int RED = 1;
int GREEN = 2;
int BLUE = 3;
int BLACK = 4;
void fill(int color);

}

Given Listings2-42 and 2-44 , youcandeclarethatthe Point and Circle classes
implementbothinterfacesbyspecifying class Point implements Drawable,
Fillable and class Circle implements Drawable, Fillable . You
canthenmodifythe main() methodtoalsotreatthedrawablesas fillables sothatyou
can fill these shapes, as follows:
public static void main(String[] args)
{

Drawable[] drawables = new Drawable[] { new Point(10,
20),

new Circle(10,

20, 30) };
for (int i = 0; i < drawables.length; i++)
drawables[i].draw(Drawable.RED);
Fillable[] fillables = new Fillable[drawables.length];
for (int i = 0; i < drawables.length; i++)
{