Programming C#, Third Edition

The Root of All Classes: Object

All C# classes, of any type, are treated as if they ultimately derive from System.Object. Interestingly, this includes value types.

A base class is the immediate “parent” of a derived class. A derived class can be the base to further derived classes, creating an inheritance “tree” or hierarchy. A root class is the topmost class in an inheritance hierarchy. In C#, the root class is Object. The nomenclature is a bit confusing until you imagine an upside-down tree, with the root on top and the derived classes below. Thus, the base class is considered to be “above” the derived class.

Tip

C and C++ programmers take note: C# uses single inheritance with a monolithic class hierarchy: every class inherits from a base class of Object, and multiple inheritance is not possible. However, C# interfaces provide many of the benefits of multiple inheritance. (See Chapter 8 for more information.)

Object provides a number of methods that subclasses can and do override. These include Equals( ) to determine if two objects are the same; GetType( ), which returns the type of the object (discussed in Chapter 8); and ToString( ), which returns a string to represent the current object (discussed in Chapter 10). Table 5-1 summarizes the methods of Object.

Table 5-1. The methods of Object

Method	What it does
Equals( )	Evaluates whether two objects are equivalent.
GetHashCode( )	Allows objects to provide their own hash function for use in collections (see