Stephens' C# Programming with Visual Studio® 2010 24-Hour Trainer

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LESSON 23 Defining Classes

from Employee. In addition to whatever features the Employee class provides, Manager adds new

DepartmentName and DirectReports properties.

class Employee : Person

{

public string DepartmentName { get; set; }

public List<Employee> DirectReports = new List<Employee>();

}

Note that C# only supports single inheritance. That means a class can inherit

from at most one parent class. For example, if you define a

House class and a

Boat class, you cannot make a HouseBoat class that inherits from both.

POLYMORPHISM

Polymorphism is a rather confusing concept that basically means a program can treat an object as if

it were any class that it inherits. Another way to think of this is that polymorphism lets you treat an

object as if it were any of the classes that it is. For example, an

Employee is a kind of Person so you

should be able to treat an

Employee as a Person.

Note that the reverse is not true. A

Person is not necessarily an Employee (it could be a Customer

or some other unrelated person).

For a more detailed example, suppose you make the

Person, Employee, and Manager classes

and they inherit from each other in the natural progression:

Employee inherits from Person and

Manager inherits from Employee.

Now suppose you write a method that takes a

Person as a parameter. Employee inherits from

Person so you should be able to pass an Employee into this method and the ...