CHAPTER 17 ■ INTERFACES

Implementing an Interface

Only classes or structs can implement an interface. As shown in the Sort example, to implement an interface, a class or struct must

•Include the name of the interface in its base class list

•Supply implementations for each of the interface’s members

For example, the following code shows a new declaration for class MyClass, which implements interface IMyInterface1, declared in the previous section. Notice that the interface name is listed in the base class list after the colon and that the class provides the actual implementation code for the interface members.

Some important things to know about implementing interfaces are the following:

•If a class implements an interface, it must implement all the members of that interface.

•If a class is derived from a base class and also implements interfaces, the name of the base class must be listed in the base class list before any interfaces, as shown here:

class Derived : MyBaseClass, IIfc1, IEnumerable, IComparable

{

...

}

416

CHAPTER 17 ■ INTERFACES

Example with a Simple Interface

The following code declares an interface named IIfc1, which contains a single method named PrintOut. Class MyClass implements interface IIfc1 by listing it in its base class list and supplying a method named PrintOut that matches the signature and return type of the interface member. Main creates an object of the class and calls the method from the object.

This code produces the following output:

Calling through: object

417