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Constructors and Destructors in C#
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A constructor is a method, which is called when an object of a class type
is constructed, and it usually used for initialization. A constructor method has
following characteristics:
- It has the same name as class
- It has no return type
- It does not return any value
- Constructors are always public and we use them to initialize variable.
- There is default class constructor without parameter, provided by C# internally if we did not write any constructor.
Note : You can declare private constructors also, when you don't want to allow clients to directly handle your class.
/* This Example is a part of different
* examples shown in Book:
* C#2005 Beginners: A Step Ahead
* Written by: Gaurav Arora
* Reach at : gaurav.aroraose@yahoo.co.in*/
// File name : privateconstructor.cs
using System;
namespace CSharp.AStepAhead.privateconstructor
{
class privateconstructor
{
private privateconstructor()
{
//This constructor never handle from client
Console.WriteLine("This is a private constructure, can't access outside");
}
public privateconstructor(int x, int y)
{
Console.WriteLine("This is a Public ocnstructore");
Console.WriteLine("X:{0}, Y:{1} X * Y : {2}", x, y, x * y);
}
//static void Main()
//{
// //Create an object of class
// privateconstructor objClass;
// objClass = new privateconstructor();
// objClass = new privateconstructor(4, 5);
// Console.ReadLine();
//}
}
class class1
{
static void Main()
{
//Create an object of class
privateconstructor objClass;
//objClass = new privateconstructor();//Neevr access from here
objClass = new privateconstructor(4, 5);
Console.ReadLine();
}
}
}
Static Constructors
Static constructors are automatically initialize when class initializes, we can
directly use the class members without creating the instance of that class
/* This Example is a part of different
* examples shown in Book:
* C#2005 Beginners: A Step Ahead
* Written by: Gaurav Arora
* Reach at : gaurav.aroraose@yahoo.co.in*/
// File name : privateconstructor.cs
using System;
namespace CSharp.AStepAhead.privateconstructor
{
class privateconstructor
{
private privateconstructor()
{
//This constructor never handle from client
Console.WriteLine("This is a private constructure, can't access outside");
}
public privateconstructor(int x, int y)
{
Console.WriteLine("This is a Public ocnstructore");
Console.WriteLine("X:{0}, Y:{1} X * Y : {2}", x, y, x * y);
}
//static void Main()
//{
// //Create an object of class
// privateconstructor objClass;
// objClass = new privateconstructor();
// objClass = new privateconstructor(4, 5);
// Console.ReadLine();
//}
}
class class1
{
static void Main()
{
//Create an object of class
privateconstructor objClass;
//objClass = new privateconstructor();//Neevr access from here
objClass = new privateconstructor(4, 5);
Console.ReadLine();
}
}
}
In the other hand a Destructor is also called a finalizer. It is just opposite the constructor, it is a method called when the garbage collector reclaims an object.
Constructors have following characteristics:
- The name of a destructor is same as name of class
- The destructor declared with a tilde (~).
- Destructors are always public and never other than public.
- Destructors take no arguments. So, there is only one destructor per class.
- Destructors have no return type.
Similarities in Class and Structure
- Both can have constructor, methods, properties, fields, constants, enumerations, events and event handlers.
- Structures and Classes can implement interface.
- Both of them have constructors with or without parameters.
- Both can have delegates and events.
Differences in Class and Structure
- Structures are value type and classes are reference type
- Structures are stored on Stack and Classes are on heap in memory.
- Structure members can’t be declared as protected, but class member can be.
- Structures cant allow inheritance
- Structure do not require constructor while Classes require.
- Objects created from classes are terminated using Garbage Collection. Structures are not collected by GC.
- Structure variables each have their own copy of the data. In Class it is possible for two variables to reference the same object. Not possible for values of a struct type to be null. Class type value may be null.
- A structure is not permitted to declare a destructor. But, you can declare a class destructor using (~) tilde.
For more details, visit http://www.msdotnetheaven.com/ChaptersCsharp/csharplanguageii.htm#
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Responses
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| Author: InterviewsWorld 13 Aug 2008 | Member Level: Silver Points : 2 | Nice description but you have very less info about static constructor.
Static constructors have the following properties:
*
A static constructor does not take access modifiers or have parameters.
*
A static constructor is called automatically to initialize the class before the first instance is created or any static members are referenced.
*
A static constructor cannot be called directly.
*
The user has no control on when the static constructor is executed in the program.
*
A typical use of static constructors is when the class is using a log file and the constructor is used to write entries to this file.
*
Static constructors are also useful when creating wrapper classes for unmanaged code, when the constructor can call the LoadLibrary method.
know more...go here
http://www.interviewsworld.com
http://msdn.microsoft.com/en-us/library/k9x6w0hc(vs.80).aspx
| | Author: Gaurav Arora 13 Aug 2008 | Member Level: Gold Points : 1 | Hi Interviewworlds,
Thanks for updation. The motive of above article is to describe imlementation of constructors.
Thanks & regards,
Gaurav Arora
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