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OOPs Concepts and .NET Part 1: Classes, Objects, and Structures

Posted by Erika Ehrli Articles | Visual C# June 22, 2005
The following article kicks off a three-part article series that will present definitions and samples for different Object-Oriented Programming concepts and its implementation in .NET. The first part will examine the concepts of classes, objects, and structures. The second part will examine the concepts of inheritance, abstraction, and polymorphism. The third and last part will examine the concepts of interface, multiple interface inheritance, collections, and overloading.
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Summary

The following article kicks off a three-part article series that will present definitions and samples for different Object-Oriented Programming concepts and its implementation in .NET. The first part will examine the concepts of classes, objects, and structures. The second part will examine the concepts of inheritance, abstraction, and polymorphism. The third and last part will examine the concepts of interface, multiple interface inheritance, collections, and overloading.

Introduction

Object-Oriented Programming (OOP) is a software development paradigm that suggests developers to split a program in building blocks known as objects. The OOP paradigm allows developers to define the object's data, functions, and its relationship with other objects.

Microsoft created the .NET Framework using OOP, and knowing this concepts has helped me to understand the .NET Framework and to design and develop better software components. The purpose of this article is to describe the basic OOP concepts using real world scenarios and to provide some code samples that demonstrate how to work with OOP and .NET.

Class

The most common definition states that a class is a template for an object. Suppose that someone builds a paper pattern for a shirt. All the shirts done with the same paper pattern will be identical (same design, size, etc.). In this sample, the paper pattern is the class and the shirt is the object. To build the same exact shirt over and over, you need the paper pattern as a template. Another great example are house plans and blueprints. The plans and blueprints define the number of rooms, the size of the kitchen, the number of floors, and more. In this real world sample, the house plans and blueprints are the class and the house is the object. In OOP you program a class as a template for a specific object or groups ob objects that will always have the same features.

Class members

A class has different members, and developers in Microsoft suggest to program them in the following order:

  • Namespace: The namespace is a keyword that defines a distinctive name or last name for the class. A namespace categorizes and organizes the library (assembly) where the class belongs and avoids collisions with classes that share the same name.
  • Class declaration: Line of code where the class name and type are defined.
  • Fields: Set of variables declared in a class block.
  • Constants: Set of constants declared in a class block.
  • Constructors: A method or group of methods that contains code to initialize the class.
  • Properties: The set of descriptive data of an object.
  • Events: Program responses that get fired after a user or application action.
  • Methods: Set of functions of the class.
  • Destructor: A method that is called when the class is destroyed. In managed code, the Garbage Collector is in charge of destroying objects; however, in some cases developers need to take extra actions when objects are being released, such as freeing handles or deallocating unmanaged objects. In .NET, there is no concept of deterministic destructors. The Garbage Collector will call the Finalize() method at a non-deterministic time while reclaiming memory for the application.

Access keywords

Access keywords define the access to class members from the same class and from other classes. The most common access keywords are:

  • Public: Allows access to the class member from any other class.
  • Private: Allows access to the class member only in the same class.
  • Protected: Allows access to the class member only within the same class and from inherited classes.
  • Internal: Allows access to the class member only in the same assembly.
  • Protected internal: Allows access to the class member only within the same class, from inherited classes, and other classes in the same assembly.
  • Static: Indicates that the member can be called without first instantiating the class.

The following sample code illustrates a sample class in C#:

///Imported namespaces
using
System;
///
Namespace: Consider using CompanyName.Product.ComponentType
namespace
DotNetTreats.OOSE.OOP_CSharp {
///
Class declaration
public class
employee {
///
Fields
private string
_name;
private int
_salary;
///
Constants
private const int
anualBonus = 1000;
///
Constructor
public
employee(){
}
///
Properties
public string
Name {
get
{
return
_name;
}
set
{
_name =
value
;
}
}
public int
Salary {
get
{
return
_salary;
}
set
{
_salary =
value
;
}
}
///
Event handlers
public event
EventHandler OnPromotion {
add {
}
remove {
}
}
///
Methods
public void
DuplicateSalary()
{
_salary = _salary*2;
}
}
}

Listing 1. Sample class implementation in C#

The following sample code illustrates a sample class in VB.NET:

'Imported namespaces
Imports
System
' Namespace: Consider using CompanyName.Product.ComponentType
Namespace
DotNetTreats.OOSE.OOP_VBNET
'Class declaration
Public Class
employee
'Fields
Private _name As
String
Private _salary As
Integer
'Constants
Private Const anualBonus As Integer
= 1000
'Constructors
Public Sub New
()
MyBase
.New()
End
Sub
'Properties
Public Property Name() As
String
Get
Return
_name
End
Get
Set(ByVal Value As String
)
_name = value
End
Set
End
Property
Public Property Salary() As
Integer
Get
Return
_salary
End
Get
Set(ByVal Value As Integer
)
_salary = value
End
Set
End
Property
' Event handlers
Public Event OnPromotion As
EventHandler
'Methods
Public Sub
DuplicateSalary()
_salary = (_salary * 2)
End
Sub
End
Class
End Namespace

Listing 2. Sample class implementation in VB.NET

Object

Objects are the building blocks of OOP and are commonly defined as variables or data structures that encapsulate behavior and data in a programmed unit. Objects are items that can be individually created, manipulated, and represent real world things in an abstract way.

Object composition

Every object is composed by:

  • Object identity: Means that every object is unique and can be differentiated from other objects. Each time and object is created (instantiated) the object identity is defined.
  • Object behavior: What the object can do. In OOP, methods work as functions that define the set of actions that the object can do.
  • Object state: The data stored within the object at any given moment. In OOP, fields, constants, and properties define the state of an object.

Structures

Not everything in the real world should be represented as a class. Structures are suitable to represent lightweight objects. Structures can have methods and properties and are useful for defining types that act as user-defined primitives, but contain arbitrary composite fields. The .NET Framework defines some structures such as System.Drawing.Rectangle, System.Drawing.Point, and System.Drawing.Color.

The following code sample represents a structures in C#:

struct Point
{
private int
_x;
private int
_y;
Point(
int x, int
y)
{
this
._x = x;
this
._y = y;
}
public int
X
{
get

{
return
_x;
}
set

{
_x =
value
;
}
}
public int
Y
{
get

{
return
_y;
}
set

{
_y =
value
;
}
}
}

Listing 3. Sample structure implementation in C#

The following code sample represents a structure in VB.NET:

Structure Point
Private _x As
Integer
Private _y As
Integer
Sub New(ByVal x As Integer, ByVal y As Integer
)
MyBase
.New()
Me
._x = x
Me
._y = y
End
Sub
Public Property X() As
Integer
Get
Return
_x
End
Get
Set(ByVal Value As Integer
)
_x = value
End
Set
End
Property
Public Property Y() As
Integer
Get
Return
_y
End
Get
Set(ByVal Value As Integer
)
_y = value
End
Set
End
Property
End Structure

Listing 4. Sample structure implementation in VB.NET

Conclusion

OOP is full of abstract concepts, and the best approach to understand them is practical and not only theoretical. I learned more OOP after making some designs and after implementing some components. The concepts presented in this article might clarify the meaning, but I strongly recommend to go and have fun playing around with OOP. In this article, I examined the concept of classes, objects, and structs. The second part will examine the concepts of inheritance, abstraction, and polymorphism.

Reference

  • Matt Weisfeld, The Object-Oriented Thought Process, SAMS, 2000.
  • Don Box, Chris Sells, Essential .NET, Addison-Wesley, 2002.

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