September 5, 2020

Programmingempire

In this post, I will answer the question When should We Use Private Constructors? For the basic information on private constructors, you can read this post on Private and Static Constructors in C#.

As you already know the basic purpose of defining a constructor in a class is to create the instance of that class. Further, as we generally instantiate a class, outside of its own definition, we declare constructors as public.

But you must remember that a class is a concept in an object-oriented paradigm and the objects are the real-world entities that have ceratin features and a well-defined behavior. Still, there are many applications in which we don’t deal with real-world objects. However, object-oriented languages like C# make it mandatory to write the code in a class only.

To illustrate further, suppose we want to create a class which provides several mathemetical functions. These functions are mostly static and called with the name of class and dot operator. This class of mathematical operationss doesn’t represent any real-world entity. In such case, we should restrict user to create an object of this class. Therefore, we should make the constructor private in such case.

Consider another example of a class that contains functions for computing factorial of a number.

using System;
namespace PrivateConstructorDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine(FactorialFunctions.Factorial(6));
      Console.WriteLine(FactorialFunctions.RecursiveFactorial(9));
        }
    }
    class FactorialFunctions
    {
        public static int Factorial(int v)
        {
            int fact = 1;
            if (v == 0) return 1;
            for (int i = 1; i <= v; i++)
            {
                fact = fact * i;
            }
            return fact;
        }

        public static int RecursiveFactorial(int v)
        {
            if (v == 0)
                return 1;
            else
                return v * RecursiveFactorial(v - 1);
        }
    }
}

The class FactorialFunctions contains only two static methods. Now, let us create object of this class:

 static void Main(string[] args)
        {
            FactorialFunctions ob = new FactorialFunctions();
            Console.WriteLine(FactorialFunctions.Factorial(6));
            Console.WriteLine(FactorialFunctions.RecursiveFactorial(9));
        }

The above code will compile without error since the compiler provides a default constructor to a class if the programmer doesn’t define one. However, it doesn’t make sense to instantiate this class, since it doesn’t have any non-static member. Therefore, by making the constructor private, we can prevent creating an instance of this class, as shown below.

using System;
namespace PrivateConstructorDemo
{
    class Program
    {
        static void Main(string[] args)
        {
           // FactorialFunctions ob = new FactorialFunctions();
            Console.WriteLine(FactorialFunctions.Factorial(6));
            Console.WriteLine(FactorialFunctions.RecursiveFactorial(9));
        }
    }
    class FactorialFunctions
    {
        FactorialFunctions() { }
        public static int Factorial(int v)
        {
            int fact = 1;
            if (v == 0) return 1;
            for (int i = 1; i <= v; i++)
            {
                fact = fact * i;
            }
            return fact;
        }

        public static int RecursiveFactorial(int v)
        {
            if (v == 0)
                return 1;
            else
                return v * RecursiveFactorial(v - 1);
        }
    }

Now, let us summarize important points regarding the usage of private constructors.

We can use private constructor in a class if it has no instance member.
Use of private constructor prevents a class from being inherited.
Private constructors are used to create a singleton class.
If a class contains static factory methods to create instance of that class, then it should have private constructors.

n this post, I will answer the question When should We Use Private Constructors? For the basic information on private constructors, you can read this post on Private and Static Constructors in C#.

Consider another example of a class that contains functions for computing factorial of a number.

using System;
namespace PrivateConstructorDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine(FactorialFunctions.Factorial(6));
      Console.WriteLine(FactorialFunctions.RecursiveFactorial(9));
        }
    }
    class FactorialFunctions
    {
        public static int Factorial(int v)
        {
            int fact = 1;
            if (v == 0) return 1;
            for (int i = 1; i <= v; i++)
            {
                fact = fact * i;
            }
            return fact;
        }

        public static int RecursiveFactorial(int v)
        {
            if (v == 0)
                return 1;
            else
                return v * RecursiveFactorial(v - 1);
        }
    }
}

The class FactorialFunctions contains only two static methods. Now, let us create object of this class:

 static void Main(string[] args)
        {
            FactorialFunctions ob = new FactorialFunctions();
            Console.WriteLine(FactorialFunctions.Factorial(6));
            Console.WriteLine(FactorialFunctions.RecursiveFactorial(9));
        }

using System;
namespace PrivateConstructorDemo
{
    class Program
    {
        static void Main(string[] args)
        {
           // FactorialFunctions ob = new FactorialFunctions();
            Console.WriteLine(FactorialFunctions.Factorial(6));
            Console.WriteLine(FactorialFunctions.RecursiveFactorial(9));
        }
    }
    class FactorialFunctions
    {
        FactorialFunctions() { }
        public static int Factorial(int v)
        {
            int fact = 1;
            if (v == 0) return 1;
            for (int i = 1; i <= v; i++)
            {
                fact = fact * i;
            }
            return fact;
        }

        public static int RecursiveFactorial(int v)
        {
            if (v == 0)
                return 1;
            else
                return v * RecursiveFactorial(v - 1);
        }
    }

Now, let us summarize important points regarding the usage of private constructors.

We can use private constructor in a class if it has no instance member.
Use of private constructor prevents a class from being inherited.
Private constructors are used to create a singleton class.
If a class contains static factory methods to create instance of that class, then it should have private constructors.

Programmingempire

Now, let us summarize important points regarding the usage of private constructors.

Now, let us summarize important points regarding the usage of private constructors.

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