Case study – drawing shapes

Let's finish off this chapter with a more practical example of using inheritance. The task is to be able to calculate the area and the perimeter of different shapes, as well as to draw them, while reusing as much code as possible.

Analysis

Let's have one Shape constructor that contains all of the common parts. From there, let's have Triangle, Rectangle, and Square constructors, all inheriting from Shape. A square is really a rectangle with the same-length sides, so let's reuse Rectangle when building the Square.

In order to define a shape, you'll need points with x and y coordinates. A generic shape can have any number of points. A triangle is defined with three points, a rectangle (to keep it simpler)—with one point and the lengths of the sides. The perimeter of any shape is the sum of its sides' lengths. Calculating the area is shape-specific and will be implemented by each shape.

The common functionality in Shape would be:

• A draw() method that can draw any shape...