Learning C# 3.0

Chapter 13: Interfaces

Quiz Solutions

Solution to Question 13-1. The interface defines the methods, properties, and so forth that the implementing class must provide. The implementing class provides these members and, optionally, additional members.

Solution to Question 13-2. Every class has exactly one base class (either explicit, or the object class by default), but may implement zero, one, or more interfaces. An abstract base class serves as the base to a derived class that must implement all of its abstract methods; otherwise, that derived class is also abstract.

Solution to Question 13-3. You can’t create an instance of an interface. To access the interface methods, you must create an instance of a class that implements the interface.

Solution to Question 13-4. You’d use the following syntax to create a class that inherits from a parent and implements two interfaces:

class MyClass : MyBase, ISuppose, IDo {...}

Note that the base class must come first after the colon.

Solution to Question 13-5. The is and as operators are used to test whether a class implements an interface.

Solution to Question 13-6. is returns a Boolean, which is false if the interface is not implemented. as attempts to make the cast, unlike is, and returns null if the cast fails. Using the as operator can be more efficient.

Solution to Question 13-7. Extending an interface is very much like deriving a class. The new interface inherits all the members of the parent interface, and can also include additional methods. ...