BİL527 – Bilgisayar Programlama I

1. BİL527– Bilgisayar Programlama I Object-Oriented Programming

2. Contents • Object-Oriented Programming • Objects • Constructors, Destructors • OOP Techniques (Interfaces, Inheritance, Polymorphism, Operator Overloading, Events)

3. Object-Oriented Programming (OOP)

4. Contents • What is OOP? • OOP Techniques • Using OOP in Console Application

5. What is OOP? • The type of programming we have covered so far is known as functional (or procedural) programming • OOP is an approach to creating computer applications which uses objects • Code reuse is easier in OOP • We have already used some objects in our programs (e.g. Console, Exception, etc.)

6. Objects • An object has both member variables and methods • structs in C contain only member variables • Objects are instantiatedfrom classes • Objects are also called instances • The terms classand objectare often confused, and it is important to understand the distinction

7. Class vs. Object Class Object Object is the implementation Objects are createdat runtime You can create many objects from a class Objects are concrete • Class is only a definition • Classes are codedin source files • You write a class once • Classes are abstract

8. Class vs. Object

9. Everything is an object • Everything in C# and .NET Framework is an object! • even the intvariables are objects too!

10. Object Members • Properties • Data contained in an object • Determine the stateof the object • They may be read-only, write-only, or both readable and writable • Example: Columbian filter coffee with milk and two sugars • Methods • Functions of objects are called methods • Example: AddSugar(), Mix(), etc.

11. Visibility • public • Public variables or methods are accessible by other objects • private • Private variables or methods are accessible only by the methods of the object itself

12. The Life Cycle of an Object • Construction • Initialization of the object • Implemented by constructors • There may be several constructors • The code snippet ctorcan be used to create a constructor in Visual Studio • Destruction • Resources used by the object are freed • Implemented by a destructorfunction • Each class may have only one destructor function

13. Construction • CupOfCoffeemyCup = new CupOfCoffee(); • CupOfCoffeemyCup = new CupOfCoffee(“Columbian”); • CupOfCoffeemyCup = new CupOfCoffee(“Columbian”, true, true, 2); Source Filtered? Milk? Sugar?

14. Constructor Syntax class MyClass { public MyClass() { // Default constructor code } public MyClass(intmyInt) { // Non-default constructor code } }

15. Destruction • You can make some extra operations when an object is about to be destroyed • e.g. Saving the object data into a file • Generally the default destructor does all the work for you and you don’t need to write a destructor

16. Destructor Syntax class MyClass { ~MyClass() { // Destructor body } } • Use the Finalize() method to call the destructor

17. Static and Instance Class Members • Static Members • Sharedbetween all instances of a class • You don’t need to instantiate an object to use a static member • You can access static member with the classname • Examples: Math.Sin(), Main(), Console.WriteLine(), int.Parse(), Convert.ToDouble(), etc. • static methods can access only the static members of a class • Instance Members • All objects have separate instance members • Instance members require an instance to be used • You can access instance members with the name of the objects • Examples: Length() (of strings and arrays), ToString(), etc.

18. OOP Techniques • Interfaces • Inheritance • Polymorphism • Operator Overloading • Events

19. Interfaces • An interface is a collection of methods and properties that are grouped together to encapsulate specific functionality • Interfaces are only some definitions, and they should be implemented in classes • i.e. the class supports all functionality defined in the interface • You can’t instantiate an interface • Interfaces cannot contain any code • Interface names generally start with ‘I’ • A class may implement more than one interfaces

20. Interface Syntax public interfaceIMyInterface { … } public class MyClass: IMyInterface { … }

21. Exercise: Sorting Cars • Create an enumeration of ‘CarBrands’ • Create a class ‘Car’ • Add two members, ‘Brand’ and ‘Price’ to ‘Car’ class definition • Create a constructor (use ‘ctor’ code snippet) • Create a ‘Display()’ method in ‘Car’ class • Create an array of cars in Main • Change ‘Car’ definition so that it implements IComparable interface • IComparable objects can be sorted • Implement the CompareTo() method • Sort the cars in Main

22. Implementing an Interface in VS

23. Solution (Page 1) enumCarBrand { Mercedes, BMW, Honda, Toyota, Volkswagen, Mazda } class Car : IComparable<Car> { // Properties: CarBrand Brand; decimal Price; // Constructor: public Car(CarBrand brand, decimal price) { this.Brand = brand; this.Price = price; } // Methods public void Display() { Console.WriteLine(this.Brand + " - " + this.Price + " TL."); } public intCompareTo(Car other) { return (int)this.Price - (int)other.Price; } }

24. Solution (Page 2) classProgram { staticvoid Main(string[] args) { Car[] cars = new Car[] { new Car(CarBrand.Volkswagen, 70000), new Car(CarBrand.Mercedes, 100000), new Car(CarBrand.Honda, 65000) }; Array.Sort(cars); Console.WriteLine("Cars sorted in price:\n"); foreach (Car car in cars) { car.Display(); } } }

25. Inheritance • Any class may inheritfrom another • Inherited class will have all members of base class • Classes in C# may derive only from a single base class directly (No multiple-inheritance) • Interfaces may inherit from other interfaces (maybe multiple) • Syntax: class InheritedClass : BaseClass { … }

26. Inheritance Syntax public class MyClass: BaseClass { … } class MyClass : BaseClass, Interface1, Interface2 { … }

27. Visibility in Inheritance • Publicmembers of the base class are accessible from the derived class • Privatemembers of the base class are not accessible from the derived class • Protectedmembers of the base class are accessible from the derived class but not accessible from other classes

28. Virtual Members • Virtualmembers of the base class can be overridden by the derived class

29. Abstract Classes • Abstract classes can’t be instantiated directly • You have to derive another class from the abstract class and then the derived class can be instantiated • Abstract classes may have abstract members, which have no implementation in the base class, so an implementation must be supplied in the derived class

30. Sealed Classes • A sealed class may not be used as a base class, so no derived classes are possible

31. Polymorphism • Using the same method with different implementations in base and derived classes is called polymorphism • Example: ToString() method of the Objectclass

32. Operator Overloading if (carA.Price > carB.Price) { … } • You can use the following code if you overload the < and > operators: if (carA > carB) { … }

33. Events • When you click a button or move the mouse in a Windows program, eventsare raised • When an event is raised, an event handler method is executed • You can add custom events into your own classes

34. Reference Types vs. Simple Types • Simple Types • int, float, double, etc. • string • object • struct • Reference Types: Contents are stored in a separate memory location (heap) • Classes (Objects created with the newkeyword) • Arrays

35. Shallow Copying vs. Deep Copying • Shallow Copying • When you make a copy of an object, value types are copied correctly but reference types point to the previous copies • Accomplished by MemberwiseClonemethod of the objectclass • MemberwiseClone() is a protectedmember of the object class • Deep Copying • Reference types are copied too • Implement the ICloneableinterface

36. Properties • You can’t make range-check on public members • Age of a person can only be positive • If negative values are assigned, program may crash • By using properties, you can check values before they are assigned • You can create read-only or write-only properties

37. Properties Syntax public intMyIntProp { get { // Property get code. } set { // Property set code. } }

38. Properties Example private intm_Age; public intAge { get{ return m_Age; } set{ if (value < 0) m_Age= 0; else m_Age = value; } }

39. Read-Only Property Example private string FirstName; private string LastName; public string FullName { get{ return FirstName + “ ” + LastName; } }

40. .:. Application .:. • Create a Curveclass which stores a list of points • Create a Pointclass to be used in the Curveclass • Add PrintPoints() and AddPoint() methods into the Curveclass • Make the Curveclass cloneable • try shallowand deepcopies • Create a propertynamed CurveLength • Overload the ‘–’operator so that Point1 – Point2 gives the distance between them • Overload the ‘<’and ‘>’operators for the Curveclass which compares the curve lengths