Advanced OOP Concepts

1. Advanced OOP Concepts 6.00 Apply Advanced Object-Oriented Programming Concepts

2. Abstract Class & Interfaces 6.04 Understand abstract classes and interfaces. (3%)

3. What is an Abstract Class? • Use the abstractmodifier in a class declaration to indicate that a class is intended only to be a base class of other classes. • Abstract classes have the following features: • An abstract class cannot be instantiated. • An abstract class may contain abstract methods and accessors. • It is not possible to modify an abstract class with the sealed modifier, which means that the class cannot be inherited. • A non-abstract class derived from an abstract class must include actual implementations of all inherited abstract methods and accessors.

4. Abstract Class Example • Create the class with the keyword abstract

5. An abstract class cannot be instantiated • This means you will NOT construct an object from an abstract class. • Given abstract class A { public abstract void aMethod() {} } • You cannot A objectA = new A(); • Why? Because there is NO implementation. • An abstract class is basically a template shell

6. An Abstract Class may Contain Abstract Methods and Accessors • Use the abstract modifier in a method or property declaration to indicate that the method or property does not contain implementation. • This means there is no code inside the method’s {}’s. • Abstract methods have the following features • An abstract method is implicitly a virtual method. • Abstract method declarations are only permitted in abstract classes. • Because an abstract method declaration provides no actual implementation, there is no method body; the method declaration simply ends with a semicolon and there are no braces ({ }) following the signature.public abstract void MyMethod();

7. Non-abstract Class Derived from an Abstract Class • A non-abstract class derived from an abstract class must include actual implementations of all inherited abstract methods and accessors. • This means that the methods must be completed for each abstract method from the abstract base class.

8. Check Your Understanding • Which of the following statements would create a C# interface? • public PlayerClass • interface public PlayerClass • public PlayerClass: interface • public interface PlayerClass

9. Check Your Understanding • Which statement would tell the compiler that the Warrior class implements the PlayerClass? • public class Warrior : PlayerClass • public class PlayerClass : Warrior • public class Warrior implements PlayerClass • public class PlayerClassimplements Warrior

10. Check Your Understanding • If the PepperGameclass implements the VeggieGameclass, which of the following uses that relationship in the Update method of the PepperGameclass? • public override void Update() • public void Update (VeggieGame game) • override public void Update (VeggieGame game) • public override void Update (VeggieGame game)

11. What is an Interface? • Interfaces describe a group of related functionalities that can belong to any class or struct. • You define an interface by using the interface keyword. interface IEquatable<T> {bool Equals(T obj); }

12. What is an Interface? • Interfaces consist of methods, properties, events, indexers, or any combination of those four member types. • An interface cannot contain constants, fields, operators, instance constructors, destructors, or types. • It cannot contain static members. • Interfaces members are automatically public, and they cannot include any access modifiers.

13. Interfaces in Derived Classes • When a class or struct implements an interface, the class or struct provides an implementation for all of the members defined by the interface. • The interface itself provides no functionality that a class or struct can inherit in the way that base class functionality can be inherited. • However, if a base class implements an interface, the derived class inherits that implementation. • The derived class is said to implement the interface implicitly.

14. Interface vs. Base Class • Classes and structs implement interfaces in a manner similar to how classes inherit a base class or struct, with two exceptions: • A class or struct can implement more than one interface. • When a class or struct implements an interface, it receives only the method names and signatures, because the interface itself contains no implementations

15. Abstract Class or Interface • Abstract Class • An abstract class is a class that cannot be instantiated, but must be inherited from. • An abstract class may be fully implemented, but is more usually partially implemented or not implemented at all, thereby encapsulating common functionality for inherited classes. • Interface • An interface, by contrast, is a totally abstract set of members that can be thought of as defining a contract for conduct. • The implementation of an interface is left completely to the developer. http://msdn.microsoft.com/en-us/library/scsyfw1d(v=vs.71).aspx

16. Abstract Class or Interface Abstract Class Interface If the functionality you are creating will be useful across a wide range of disparate objects If you are designing small, concise bits of functionality • If you anticipate creating multiple versions of your component • If you are designing large functional units • If you want to provide common, implemented functionality among all implementations of your component