Summary:
As a programmer, java is all about classes and there are design patterns that we must follow, and it is our duty to question them. Java is an object orientated programming language where we have the ability to write our code in the form of reusable classes. Code re-usability doesn’t start by creating objects out of classes, it starts way before that when we are creating the classes itself. The class types that we have available to us are Interface, Abstract, and Concrete classes.
Reason:
The reason why I chose this article was because I thought this article would help us understand why we us certain classes and when to use them. In class we have gone over different design patterns where the uses of every class are different depending on what we want to achieve. I believe that it is important to fully understand how they each function as it will make understanding the design patterns much easier.
What I’ve Learned:
Interfaces are a blueprint for your class that can be used to implement a class and an interface cannot have any concrete methods. What your interface can have are static members and method signatures. All methods that you declare in an interface can have static, default or abstract modifiers. Abstract methods cannot have a body; all they can have is a method signature. Variables are not allowed in interface. Hence any data declaration is public static final. Interfaces can extend other interfaces (one or more) but not classes (abstract or not). Interfaces cannot be instantiated as they are not concrete classes. Methods and constants cannot be declared private, methods cannot be declared final.
Abstract classes are a bit different from interfaces. These are also used to create blueprints for concrete classes but abstract classes may have implemented methods. Abstract classes can implement one or more interfaces and can extend one abstract class at most. A class can be an abstract class without having any methods inside it. But if it has any methods inside it, it must have at least one abstract method. This rule does not apply to static methods. As abstract classes can have both abstract and non abstract methods. Static members are allowed. Abstract classes can extend other at most one abstract or concrete class and implement several interfaces. Any class that does not implement all the abstract methods of it’s super class has to be an abstract class itself.
Concrete classes are the usual stuff that every java programmer has come across for sure. It is like the final implementation of a blueprint in case you are extending it some abstract super class. A concrete class is complete in itself and can extend and can be extended by any class. The only condition is that all the methods have to be implemented in order for it to qualify as a concrete class.
From the blog CS@Worcester – Life as a CS Student by Dylan Nguyen and used with permission of the author. All other rights reserved by the author.

