The PaintBox Project - Java Software Solutions: Foundations of Program Design - page 710

Rectangle class from the Java standard class library, but on further investigation
we realize that its role is not really consistent with our goals. In addition, no other
classes are defined for the other shapes we need.
So, as we envisioned in our architectural design, we consider having one
class per shape type: Line , Oval , Rect , and Poly . Remember that circles and
squares will just be specific instances of the Oval and Rect classes, respec-
tively. Each shape class will have a draw method that draws that kind of shape
on the screen.
Now let's consider the kind of information that each shape needs to store to be
able to draw itself. A line needs two points: a starting point and an ending point.
Each polyline, on the other hand, needs a list of points to define the start and end
points of each line segment. Both ovals and rectangles are defined by a bounded
rectangle, storing an upper-left corner and the width and height of the shape.
This analysis leads to the conclusion that Oval and Rect objects have some
common characteristics that we could exploit using inheritance. They could both,
for instance, be derived from a class called BoundedShape . Furthermore, because
all shapes have to be stored in the ArrayList object that we'll use to keep track
of the entire drawing, it would simplify the refinement to have a generic Shape
class from which all drawn shapes are derived.
The Shape and BoundedShape classes are used for organizational purposes.
We do not intend to instantiate them; therefore they probably should be abstract
classes. In fact, if we define an abstract method called draw in the Shape class,
we could capitalize on polymorphism to simplify the drawing of the shapes in
the drawing area. A loop can move through the ArrayList , having each shape
(whatever it may be) draw itself.
After some consideration, we achieve the class diagram shown in Figure J.5.
This diagram specifically represents the classes that are important to the second
refinement of the PaintBox project.
Selecting a current color can be relegated to the JColorChooser component
provided by the Swing package. The color button will bring up the JColorChooser
dialog box and respond accordingly to the user's selection.
Multiple shapes will accumulate on the drawing surface. We could define a
class to serve as a collection of the drawn shape objects. It could use an ArrayList
to keep track of the list of shapes. Whenever the drawing area needs to be
refreshed, we can iterate through the list of shapes and draw each one in turn.
Figure J.6 shows the PaintBox program after the first two refinements have
been completed. Once again, we could visit with the client at this point to deter-
mine whether the evolution of the system meets with his or her satisfaction.