Programming C# 3.0, 5th Edition

Encapsulating Data with Properties

Properties allow clients to access the state of the object as though they were accessing member fields directly, while actually implementing that access through a class method.

This is ideal. The client wants direct access to the state of the object and doesn't want to work with methods. The class designer, however, wants to hide the internal state of his class in class members, and provide indirect access through a method.

By decoupling the class state from the method that accesses that state, the designer is free to change the internal state of the object as needed. When the Time class is first created, the Hour value might be stored as a member variable. When the class is redesigned, the Hour value might be computed or retrieved from a database. If the client had direct access to the original Hour member variable, the change to computing the value would break the client. By decoupling and forcing the client to go through a method (or property), the Time class can change how it manages its internal state without breaking client code.

Properties meet both goals: they provide a simple interface to the client, appearing to be a member variable. They are implemented as methods, however, providing the data-hiding required by good object-oriented design, as illustrated in Example 4-12.

Example 4-12. Using a property

using System; namespace UsingAProperty { public class Time { // private member variables private int year; private int month; private int date; ...