Object-Oriented Programming Chapter 4 Ebook: Beginning Visual C# 2010, part 1, chapter 8,9,10,13 Reference: DEITEL - CSharp How to Program Contents  Review concepts in OOP  Write classes in C#  Interface  Inheritance  Polymorphism  Relationships between objects Slide 2 Review concepts in OOP  Review concepts in OOP  class  object  field  property  method  event  Other problems  Static members: field, property and method (p.191)  Static constructor (p.191)  Static class (p.192) Slide 3 ClassName - Fields + Methods Class diagram Contents  Review concepts in OOP  Write classes in C#  Interface  Inheritance  Polymorphism  Relationships between objects Slide 4 Create a class in C# Slide 7 Member access modifiers  Without a access modifier : can be accessed by any class in the same namespace  private: can only be accessed from inside the class  public: can be accessed from anywhere  protected: can be accessed from inside the child class or any class in the same namespace Slide 8 Writing properties  Properties (accessors):  Contain two blocks: get and set the value of the fields  One of these blocks can be omitted to create read-only or write-only properties  You can use Encapsulate Field function to properties Slide 9 Writing constructors  A constructor is a special method in a class that is invoked when the object gets instantiated  A constructor is used to initialize the properties of the object  Note to write a constructor:  The name of the constructor and the name of the class are the same  A constructor does not return value, not even void  A class can have multiple constructors (overloaded constructors) public ClassName (parameterList) { } Slide 10 Instantiating an object  To instantiate an object, using the new keyword  Example: Lop l = new Lop(); Lop c; c = new Lop(“NCTH2K”, “Cao dang nghe 2K”); ClassName object = new ClassName (…); ClassName object; object = new ClassName (…); Slide 11 Using properties, methods of a class  Call methods or properties of a class  Using dot operator  Accessors:  get: variable = object.propertyName  set: object.propertyName = variable  Example: Lop c = new Lop(); c.MaLop = "NCTH2K"; // call set{} c.TenLop = "Cao dang nghe 2K"; // call set{} Slide 12 [...]... child class can redefine a base-class method; this method is called overriding method To be overridden, a base-class method must be declared vir tual To write an overriding method, using override keyword in the method header To view the method header for a method, using Object Browser  Example: view Object s methods Slide 27 Object class (p.215)  All classes inherit from Object   All classes have... Class View Window (p.222)   The Object Browser (p.2 24)   Menu View\Class View Menu View \Object Browser Class Diagrams (p.227)  The class diagram editor in VS enables you to generate UMLlike diagrams of your code and use them to modify projects Slide 13 static class members (p.191)  Every object of a class has its own copy of all instance variables  How can all objects of a class share the same... void Main( string[] args ) { Circle circle = new Circle( 37, 43 , 2.5 ); // get Circle3's initial x-y coordinates and radius string output = "X coordinate is " + circle.X + "\n" + "Y coordinate is " + circle.Y + "\nRadius is " + circle.Radius; // set Circle3's x-y coordinates and radius to new values circle.X = 2; circle.Y = 2; circle.Radius = 4. 25; // display Circle3's string representation output +=... Slide 33 Contents       Review concepts in OOP Write classes in C# Interface Inheritance Polymorphism Relationships between objects Slide 34 Polymorphism (p.196)  Polymorphism allows objects to be represented in multiple forms  Polymorphism via inheritance: All objects instantiated from a derived class can be treated as if they were instances of a parent class Cow myCow = new Cow(); Animal... the abstract methods and properties of the base-class Slide 36 Polymorphism example  Base-class Employee    Classes that derive from Employee        abstract abstract method Earnings Boss CommissionWorker PieceWorker HourlyWorker All derived-classes implement method Earnings Driver program uses Employee references to refer to instances of derived-classes Polymorphism calls the correct version...   All classes have access to the protected and public members of this class (table p.215) You can override some methods of Object class (if a method is being overridden)   Example: public override string ToString() Some Object s methods:    ToString(): example Equals (object) : example GetHashCode(): example Slide 28 Example: class Point public class Point { private int x, y; public Point()... keyword static  Static members can be fields, properties, methods  When using static members, don’t need to instantiate an object Slide 14 static class members (cont.) public class Employee { private string firstName; private string lastName; private static int count; // Employee objects in memory public Employee( string fName, string lName ) { firstName = fName; lastName = lName; count++; } public static... and methods of the parent class   A programmer can tailor a child class as needed by adding new variables or methods, or by modifying the inherited ones C# provides a common base class for all objects called Object class Slide 23 Inheritance (cont.)  Declare inheritance class public class ChildClass : ParentClass { // }   ParentClass ChildClass Classes in C# may derive only from a single base class... Constants.PI * constantValues.radius, "Circumference" ); } } Slide 19 Contents       Review concepts in OOP Write classes in C# Interface Inheritance Polymorphism Relationships between objects Slide 22 Inheritance (p.1 94)   Inheritance enables to create a new class that extends an existing class  The existing class is called the parent class, or super class, or base class  The new class is called... base class directly The protected modifier allows a child class to reference a variable or method directly in the parent class  A protected variable is visible to any class in the same namespace Slide 24 The base reference    Constructors are not inherited To invoke the parent's constructor : base (parameters); The base reference can also be used to reference other variables and methods defined in . 4 Ebook: Beginning Visual C# 2010, part 1, chapter 8,9,10, 13 Reference: DEITEL - CSharp How to Program Contents  Review concepts in OOP  Write classes in C#  Interface  Inheritance  Polymorphism. C#  Interface  Inheritance  Polymorphism  Relationships between objects Slide 2 Review concepts in OOP  Review concepts in OOP  class  object  field  property  method  event  Other problems  Static. (p.191)  Static constructor (p.191)  Static class (p.192) Slide 3 ClassName - Fields + Methods Class diagram Contents  Review concepts in OOP  Write classes in C#  Interface  Inheritance  Polymorphism