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Source Code

The EmployeeApp project can be found under the Chapter 5 subdirectory.

Summary

The point of this chapter was to introduce you to the role of the C# class type. As you have seen,

classes can take any number of 

constructors that enable the object user to establish the state of the

object upon creation. This chapter also illustrated several class design techniques (and related key-

words). Recall that the this keyword can be used to obtain access to the current object, the static

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keyword allows you to define fields and members that are bound at the class (not object) level, and

the const keyword (and readonly modifier) allows you to define a point of data that can never

change after the initial assignment.

The bulk of this chapter dug into the details of the first pillar of OOP: encapsulation. Here you

learned about the access modifiers of C# and the role of type properties, partial classes, and XML

code documentation. With this behind us, we are now able to turn to the next chapter where you

will learn to build a family of related classes using inheritance and polymorphism.

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Understanding Inheritance and

Polymorphism

T

he previous chapter examined the first pillar of OOP: encapsulation. At that time you learned

how to build a single well-defined class type with constructors and various members (fields, prop-

erties, constants, read-only fields, etc.). This chapter will focus on the remaining two pillars of OOP:

inheritance and polymorphism.

First, you will learn how to build families of related classes using 

inheritance. As you will see,

this form of code reuse allows you to define common functionality in a parent class that can be

leveraged (and possibly altered) by child classes. Along the way, you will learn how to establish a

polymorphic interface into the class hierarchies using virtual and abstract members. We wrap up by

examining the role of the ultimate parent class in the .NET base class libraries: System.Object.