Swift 3 ObjectOriented Programming - Second Edition

Organizing classes with UML diagrams

So far, our object-oriented solution includes six classes with their properties and methods. However, if we take another look at these six classes, we will notice that all of them have the same two methods: calculatedArea and calculatedPerimeter. The code for the methods in each class is different because each shape uses a special formula to calculate either the area or the perimeter. However, the declarations, contracts, 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 six classes, we said we were talking about six different geometrical shapes or simply shapes. ...