Constructor in C#

A constructor is a special method of a class or structure in object-oriented programming that initializes an object of that type. A constructor is an instance method that usually has the same name as the class, and can be used to set the values of the members of an object, either to default or to user-defined values.

Some key point of constructor

·         Constructor is member of a class and structure.

·         Constructor is a special type of function which will be fire at time of object is creating or class is load.

·         Constructor name is always same name as class name.

·         Constructor not contains any return type, because it not returns any value.

·         Constructor can contain a parameter or not.

Syntax of constructor

<Access modifier><class name (type><parameter>)>

{

Code initialization

}

Instance constructor:-While define a constructor without using static key word is known as instance constructor.

Key point

·        Only instance constructor can hold parameter

·        It initialize at the time of object is created.

·        In a single class multiple instance constructors can be created but condition is each constructor should be unique to other by using different signature and number of parameter should vary.

Static constructor

When a constructor is created as static, it will be invoked only once for all of instances of the class and it are invoked during the creation of the first instance of the class or the first reference to a static member in the class. A static constructor is used to initialize static fields of the class and to write the code that needs to be executed only once.

Key Point constructor

Ø A static constructor does not take access modifiers or have parameters.

Ø A static constructor is called automatically to initialize the class before the first instance is created or any static members are referenced.

Ø A static constructor cannot be called directly.

A default constructor is a constructor which can be called with no arguments /with any parameter. 

 Key point  

Ø Definition of the constructor outside the class body.

Ø Inhibiting the automatic generation of a default constructor by the compiler.

Ø Explicitly forcing the automatic generation of a default constructor by the compiler.

using System;
namespace DefaultConstractor
 {
    class  demo
    {
        int a, b;  // class variable declartion

        public addition()   //without  any parameter  or argument

        {

            a = 100;

            b = 175;

        }

        public static void Main()

        {

            addition obj = new addition(); 

            Console.WriteLine(obj.a);

            Console.WriteLine(obj.b);

            Console.Read();

        }

      }

    }

Parameterized Constructor:- 

A constructor with at least one parameter is called parameterized constructor. The advantage of a parameterized constructor is that you can initialize each instance of the class to different values.

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

namespace parameterizedConstuctor

{

    class Course

    {

        ulong cid;

        string cname;

        double cfees;

        internal Course(ulong CourseID, string courseName, double courseFees)

        {

            cid = CourseID;

            cname = courseName;

            cfees = courseFees;

                    }

        internal void DisplaycourseDetails()

        {

            Console.WriteLine("Course Code : " + cid);

            Console.WriteLine("Couse Name : " + cname);

            //Console.WriteLine("Couse Name : " + string.Format("{0:0.00}"+ cfees));

            // string s = string.Format("Course Fees is {0:0.00}", +cfees);

            // Console.WriteLine(s);

            Console.WriteLine( string.Format("Course Fees is {0:0.00}", +cfees));

        }

        static void Main(string[] args)

        {

            Course obj1 = new Course(101, "C# .net", 1100.00);

            obj1.DisplaycourseDetails();

            Course obj2 = new Course(102, "Angular", 7000.00);

            obj2.DisplaycourseDetails();

            Course obj3 = new Course(103, "MVC", 1100.00);

            obj3.DisplaycourseDetails();

            Console.ReadLine();

        }

    }

}