Abstract and Sealed Classes and Class Members
The abstract keyword enables you to create classes and class members that are incomplete and must be implemented in a derived class. The sealed keyword enables you to prevent the inheritance of a class or certain class members that were previously marked virtual. Abstract Classes and Class Members Classes can be declared as abstract by putting the keyword abstract before the class definition . For example: An abstract class cannot be instantiated. The purpose of an abstract class is to provide a common definition of a base class that multiple derived classes can share. For example, a class library may define an abstract class that is used as a parameter to many of its functions, and require programmers using that library to provide their own implementation of the class by creating a derived class. Abstract classes may also define abstract methods. This is accomplished by adding the keyword abstract before the return type of the method. For example: Abstract methods have no i...