BRINGING THE PIECES TOGETHER II – Interface Declaration and Implementation

In my last post, we started bringing together the pieces of our previous tutorials together – we were able to set up our IDEs, created packages, classes, variables and Identifiers. In this post, we will continue from where we stopped which was the class. Looking again at the structure of our application (AreaofShapes) as we discussed earlier here, we have three packages, nine (9) classes and one (1) interface altogether as shown below.


In the last lesson, I explained the purpose of each package and we saw the content of ShapeVariableBean and how encapsulation came to play. Today, we will focus more on the package and also, we will see how other classes implements interface within this package. In package, the shapes are divided into two; PolygonController and NonpolygonController.

Note: As an update on the last post, I added a new item on this package which is what we will be focusing on today. I added interface AllShapesInterface above so we can see how to make use of an interface in the course of these set of lessons. Before we continue, please refer to my earlier post on interface where I explained in detail what an Interface is in case you missed the lesson.

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More on Object Oriented Programming…

In my previous post, I started discussion on Object Oriented Programming click here if you missed it where I explained Encapsulation and Inheritance as OOP concepts. This post will be wrapping up this lesson with Abstraction and Polymorphism concepts.

Abstraction:This is a process whereby important details of a method are hidden and only the functionality is shown to the user. For instance, Abstraction will only tell the user things like a class can cook, wash, and fly by listing out the functions but not how the actual cooking, washing and flying are done. In Java, the ‘what a class can do’ is known as method while the ‘how the method does them’ is called Implementation. Therefore we can simply say abstraction list methods and hides implementation.

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What really is Object Oriented Programming?

Over the last couple of weeks, we have looked at Java Modifiers and Basic Java Keywords and syntax I and II. As you may already know, Java is an object oriented program (OOP). OOP (Object Oriented Programming) as a programming model involves the collection of interacting objects. An Object is a black box which contains code and data, it sends and receives messages and are used to represent real life concepts ranging from human beings (described by name, address, and so forth) to countries (whose properties can be described and managed) down to the little widgets on a computer desktop (such as buttons and scroll bars). Some of the concepts of OOP have been discussed in my earlier posts however, despite these discussions  OOP will be incomplete without explaining the following concepts:

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