When developing object-oriented applications, you've already seen how you can use classes to model business data, apply actions such as validation, and carry out calculations that may need to be performed on the data to fulfill business and behavioral rules.

However, some of your business entity types may be related. If you consider bank accounts for a moment, there are a number of different account types, some of which allow you to overdraw and offer an overdraft limit, such as a current account, and others that give interest but don't offer overdrafts, such as a savings account.

As you'll come to find out in this module you can use the object orientation concept of inheritance to manage these structures. This is done by defining a base class that contains code that is common to all the different types of account and specialist classes that extend or replace, AKA override the base class functionality.

If inheritance defines an is-a relationship, for example a BMW is a kind of car, then you would use composition to define the has-a relationship, which might be that the BMW has wheels. C# doesn't allow classes to inherit from more than one parent at a time, so as you'll come to discover later on, composition could be used as a workaround for this problem.

Returning to the world of banking as an example, you'll learn how a bank would calculate the total amount of money held within all the various account types just mentioned. As you'll see, this involves taking an object orientation approach by looking at each of the specialist account objects through their base class references and adding all their balances together.

Another important lesson in the module is understanding polymorphic behavior by again looking at objects through a base class reference, but getting the specialist behavior when an overridden method is invoked.

The module will also introduce you to the concept of abstract classes, which are classes that can't be instantiated, and interfaces, which allow you to define a set of methods and properties that a class has to implement and support.

As usual, at the end of the module you'll be offered the opportunity to put what you've learned into practice in the lab and coding challenge. Take your time to cover everything and make sure you understand it before moving on.

Understanding inheritance | C# I |

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