Thursday, 13 November 2014

Private Constructor in C#

Introduction:

Here I will explain what is private constructor in c# with example. Private constructor in c# is used to restrict the class from being instantiated when it contains every member as static.

Description:

Constructor is a special method of a class which will invoke automatically whenever instance or object of class is created. Constructors are responsible for object initialization and memory allocation of its class. If we create any class without constructor, the compiler will automatically create one default constructor for that class. There is always at least one constructor in every class. If you want to know more about constructors check this article constructors in c#.

Private Constructor

Private constructor is a special instance constructor used in a class that contains static member only. If a class has one or more private constructor and no public constructor then other classes is not allowed to create instance of this class this mean we can neither create the object of the class nor it can be inherit by other class. The main purpose of creating private constructor is used to restrict the class from being instantiated when it contains every member as static.

using System;
namespace ConsoleApplication3
{
public class Sample
{
public string param1, param2;
public Sample(string a,string b)
{
param1 = a;
param2 = b;
}
private Sample()  // Private Constructor Declaration
{
Console.WriteLine("Private Constructor with no prameters");
}
}
class Program
{
static void Main(string[] args)
{
// Here we don't have chance to create instace for private constructor
Sample obj = new Sample("Welcome","to Aspdotnet-Suresh");
Console.WriteLine(obj.param1 +" " + obj.param2);
Console.ReadLine();
}
}
}


Output

Welcome to Aspdotnet-Suresh

In above method we can create object of class with parameters will work fine. If create object of class without parameters it will not allow us create.

// it will works fine
Sample obj = new Sample("Welcome","to Aspdotnet-Suresh");
// it will not work because of inaccessability
Sample obj=new Sample();


Important points of private constructor

-      One use of private construct is when we have only static member.
-      Once we provide a constructor that is either private or public or any, the compiler will not allow us to add public constructor without parameters to the class.
-      If we want to create object of class even if we have private constructors then we need to have public constructor along with private constructor

I hope it helps to know about private constructor.

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