Classes and Inheritance - Illustrated C# 2005 - page 166

Abstract Classes
An abstract class can be used only as the base class of another class. Abstract classes are
designed to be inherited from.

￿ You cannot define variables or create instances of an abstract class.

An abstract class is declared by using the abstract modifier. ￿

Keyword
↓
abstract class MyClass
{
...
}

￿ An abstract class can contain abstract members, but that is not a requirement. The

members of an abstract class can be any combination of abstract members and
normal members with implementations.

￿ An abstract class can, itself, be derived from another abstract class. For example, the fol-

lowing code shows one abstract class derived from another.

abstract class AbClass // Abstract class
{
...
}

abstract class MyAbClass : AbClass // Abstract class derived from
{ // an abstract class
...
}

￿ Any class derived from an abstract class must implement all the abstract members of the

class by using the override keyword, unless the derived class is, itself, abstract .