Types of constructors

1. Instance Constructor
2. Static Constructor (gets called only once)
3. Private Constructor


Static Constructor

 A static constructor is used to initialize any static data or to perform a particular action that needs to be performed once automatically before the first instance is created or any static members are referenced.

E.G.

Class SimpleClass
{
static readonly long x;
//static constructor is called at most one time
//before any constructor is invoked or member is accessed

Static SimpleClass()
{
x = DateTime.Now.Ticks;
}
}

Important points to note

• A static constructor does not take access modifier or have parameters
• A static constructor cannot be called directly
• Users have no control only when the static constructor is executed in the program
• A typical use of static constructor is when the class is using a log file and constructor is used to write entries
• We can have both static constructor and instance constructor in same class

Private Constructor

If a class has one or more private constructor *and no public constructor* other class cannot create instance of this class (expect nested class).

We can have both private & public constructor in same class if parameters are different.

By default constructor is private. If we try to create instance of a class having private constructor, you will get constructor is inaccessible due to its protection level

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Unless a class is static, class without constructor are given a public default by c# compiler in order to enable class instantiation.

Moral : A class must have public constructor for creating its object

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Copy constructor : c# doesn't provide constructor  for objects, but we can create


E.g.

class Person
{
//Copy constructor
public Person (Person prevPerson)
{
Name = prevPerson.Name;
Age = prevPerson.Age
}


//Below is parameterized constructor public Person (string name, int age)
{
Person P1 = new Person("George", 40);
Person P2 = new Person (P1);
}
}