We could easily recognize objects from Pitstop's artwork. We understood that each pattern is composed of many 2D geometric shapes and we recognized the different shapes that she used in all the examples we analyzed. Now, let's focus on one of the core requirements for the Web Service, which is calculating the required amounts of acrylic paint to produce the artwork. We must take into account the following data for each 2D shape included in the pattern in order to calculate the required materials and the amount of acrylic paint to produce each shape:

It is possible to use a specific color for the line that draws the borders of each shape, and therefore, we have to calculate the perimeter to use it as one of the values that will allow us to estimate the amount of acrylic paint that the user must buy to paint the border of each 2D shape. Then, we have to calculate the area to use it as one of the values...

Imagine that we have to draw and calculate the perimeters and areas of three different rectangles. You will end up with three rectangles drawn with their widths and height values and their calculated perimeters and areas. It would be great to have a blueprint to simplify the process of drawing each rectangle with their different width and height values.

In object-oriented programming, a class is a template definition or blueprint from which objects are created. Classes are models that define the state and behavior of an object. After declaring a class that defines the state and behavior of a rectangle, we can use it to generate objects that represent the state and behavior of each real-world rectangle.

The following picture shows two rectangle instances named rectangle1 and rectangle2. These instances are drawn with their width and...

We know the information required for each of the shapes to achieve our goals. Now, we have to design the classes to include the necessary fields that provide the required data to each instance. We have to make sure that each class has the necessary fields that encapsulate all the data required by the objects to perform all the tasks based on our application domain.

Let's start with the Circle class. We need to know the radius for each instance of this class, that is, for each circle object. Thus, we need an encapsulated variable that allows each instance of the Circle class to specify the value for the radius.

So far, we designed nine classes and identified the necessary fields for each of them. Now, it is time to add the necessary pieces of code that work with the previously defined fields to perform all the necessary tasks, that is, to calculate perimeters and areas. We have to make sure that each class has the necessary encapsulated functions that process the property values specified in the objects to perform all the tasks.

Let's forget a bit about similarities between the different classes. We will work with them individually as if we didn't have the necessary knowledge of geometric formulas. We will start with the Circle class. We need pieces of code that allow each instance of this class to use the value of the radius property to calculate the area and perimeter.

So far, our object-oriented solution includes nine classes with their fields and methods. However, if we take another look at these nine classes, we will notice that all of them have the same two methods: calculateArea and calculatePerimeter. The code for the methods in each class is different because each shape uses a special formula to calculate either the area or perimeter. However, the declarations, contracts, interfaces, or protocols for the methods are the same. Both methods have the same name, are always parameterless, and return a floating point value. Thus, all of them return the same type.

When we talked about the nine classes, we said we were talking about nine different geometrical 2D shapes or simply shapes. Thus, we can generalize the required behavior, protocol, or interface for these nine shapes. The nine shapes must define the calculateArea and calculatePerimeter methods with the previously explained declarations. We can create an interface...