Visual Basic 2012 Programmer's Reference

INHERITANCE

Inheritance is the process of deriving a child class from a parent class. The child class inherits all of the properties, methods, and events of the parent class. It can then modify, add to, or subtract from the parent class. Making a child class inherit from a parent class is also called deriving the child class from the parent, and subclassing the parent class to form the child class.

For example, suppose you define a Person class that includes variables named FirstName, LastName, Street, City, State, Zip, Phone, and Email. It might also include a DialPhone method that dials the person’s phone number on the phone attached to the computer’s modem or on a voice over Internet protocol (VoIP) provider.

You could then derive the Employee class from the Person class. The Employee class inherits the FirstName, LastName, Street, City, State, Zip, Phone, and Email variables. It then adds new EmployeeId, SocialSecurityNumber, OfficeNumber, Extension, and Salary variables. This class might override the Person class’s DialPhone method, so it dials the employee’s office extension instead of the home phone number.

You can continue deriving classes from these classes to make as many types of objects as you need. For example, you could derive the Manager class from the Employee class and add fields such as Secretary that would refer to another Employee object that represents the manager’s secretary. Similarly, you could derive a Secretary class from Employee that includes a reference ...