As you probably know, classes are simply containers for related methods and properties to describe an object in your software. An object is an instance of a specific class and, sometimes, mimics real-world things. When thinking of a car, you might create a vehicle class that contains certain attributes (properties) that all vehicles contain, such as automatic or manual transmission, wheel count (not all vehicles have only four wheels), or fuel type.

When we create an instance of the vehicle class, we can create a car object, an SUV object, and so on. Here lies the power of classes, which is to describe the world around us and translate it into a programming language that a compiler can understand.

Many developers have heard about abstract classes, but their implementation is a mystery. How can you as a developer identify an abstract class and decide when to use one? The definition is quite a simple one actually. Once you understand this fundamental definition of an abstract class, when and why to use one becomes obvious.

Imagine for a moment that you are developing an application that manages the animals in a cat sanctuary. The cat sanctuary rehabilitates lions, tigers, jaguars, leopards, cheetahs, pumas, and even domestic cats. The common noun that describes all these animals is the word cat. You can, therefore, safely assume that the abstraction of all these animals is a cat, and thus, this word identifies our abstract class. You would then create an abstract class called Cat.

However, you need to keep in mind that you will never ever create an instance of the...

For many developers, interfaces are equally confusing and their purpose not clearly understood. Interfaces are actually quite easy to get to grips with once you understand the concept that defines an interface.

Interfaces act like verbs. So, for example, if we had to create two classes called Lion and Tiger that derive from the Cat abstract class, the interface would describe some sort of action. Lions and tigers can roar (but not purr). We can then create an interface called IRoarable. If we had to derive a class called Cheetah from our abstract class Cat, we would not be able to use the IRoarable interface, because cheetahs purr. We would need to create an IPurrable interface.

Creating an interface is very similar...

Generics is a very interesting way of writing code. Instead of specifying the data type of the elements in the code at design time, you can actually delay the specification of those elements until they are used in code. This basically means that your class or method can work with any data type.

We will start off by writing a generic class that can take any data type as a parameter in its constructor and do something with it.

1. Declaring a generic class is actually very easy. All that we need to do is create the class with the generic type parameter...

Generic interfaces work in much the same way as the previous examples in generics. Let's assume that we want to find the properties of certain classes in our code, but we can't be sure how many classes we will need to inspect. A generic interface could come in very handy here.

We need to inspect several classes for their properties. To do this, we will create a generic interface that will return a list of all the properties found for a class as a list of strings.

Let's take a look at the following implementation of the generic interface...