C# 5.0 Programmer's Reference

Method Declarations ❘ 125
Now suppose the Employee class is derived from Person. The Employee class adds a new Office
field and provides the following new Address method that includes the Office value.
public new string Address()
{
return FirstName + " " + LastName + ", " + Office + '\n' +
Street + '\n' +
City + " " + State + " " + Zip;
}
Without the new keyword, this would raise the warning.
static
As Chapter 4 explained, a variable declared with the static keyword is shared by all instances of
the class. Similarly, a static method applies to all instances of the class. In that case, the method
applies to the class itself rather than to a particular instance of the class.
For example, suppose the Person class has a LookupPerson method that looks up a person’s name in
a database and returns a Person object representing that person. It wouldn’t make sense to require
you to create a Person object just to invoke its LookupPerson method. Instead you can make this a
static method.
To invoke a static method, use the class name as in Person.LookupPerson("Eddie Russett").
virtual and override
The virtual keyword and override keywords go together.
Suppose the Person and Employee classes have Address methods as described in the previous
sections. The Employee class’s version of Address hides the Person class’s version. Now consider
the following code.
Employee employee = new Employee { FirstName = "Rod", ... };
Console.WriteLine("Employee:\n" + employee.Address());
Console.WriteLine();
Person person = employee;
Console.WriteLine("Person:\n" + person.Address());
The code creates an Employee object and displays the result of its Address method in the Console window.
This includes the object’s FirstName, LastName, Office, Street, City, State, and Zip values.
Next the code sets a Person variable equal to the same Employee. This is allowed because an
Employee is a kind of Person. The code then displays the result of the Person object’s Address
method. Because this is a Person object, its Address method doesn’t include the object’s Office
value. Even though this object is actually an Employee, the Person class’s version of the Address
method doesn’t include the Office value. The following text shows the result.
Employee:
Rod Stephens, B-24
1337 Leet St
Bugsville HI 98765
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