Constructor .NET

Introduction

Constructors have a very special meaning to Compiler and CLR but sometimes its flow seems difficult for a developer. Today I will explain simple but important insights of Constructor.

So, What is a Constructor?

A Constructor is a special method in a class/struct with the same name as that of class/struct without any return type, used to initialize fields and members of a class/struct;

A constructor can only be called by:

• Compiler using New keyword to initialize a class/struct.
• Another constructor of same class/struct using :this() keyword.
• Constructors of derived class using :base() keyword.

Types of Constructor in C#?

• Default constructor
• Parameterized constructor
• Instance constructor
• Static constructor
• Private constructor

Default Constructor?

1. A Constructor with no parameter is called Default Constructor.
2. Default Constructor is called by compiler when no arguments are passed to New operator while creating an object of class or struct.
3. If there is no constructor in a Non-Static class, a Public Default Constructor is provided by compiler so that a class can be instantiated.
4. A Struct cannot have an explicit Default Constructor (We cannot define an explicit Default Constructor in a struct), but it is always provided by compiler to initialize each field of struct to its default value.

Parameterized Constructor?

1. A constructor with parameters is called parameterized Constructor.
2. A Class or Struct can have multiple parameterized constructors as long as they have different method signature. They follow the same concept of method overloading.
3. Compiler provides Default Constructors only if there is no constructor (Default or Parameterized) defined in a class.
4. Parameterized Constructors can exist even without the existence of Default Constructors.

Static Constructor?

1. To initialize a Static Class or Static variables in Non-Static Class, Static Constructors are used
2. Access Modifiers are not allowed on Static Constructors
3. Static Constructors cannot be parameterized
4. There can be only one Static Constructors per class
5. Static Constructors cannot have an explicit 'this' or 'base' constructor call, i.e., Static Constructors cannot be called directly
6. Static Constructors are called automatically before the first instance of a class is created or any static member is referenced
7. Static Constructors are called only once in the lifetime of a class

Private Constructor?

1. A constructor becomes a private constructor when we declare with private access specifier.
2. Private Constructors can neither be instantiated nor inherited from other class.
3. Object of class can only be created in the class itself.
4. Microsoft recommends its uses to implement Singleton Pattern.

Constructor Chaining?

1. A constructor can make a call to another constructor of the same class or of base class;
2. Since one constructor can invoke another, this sometimes can cause execution of multiple constructors and is referred to as Constructor chaining;
3. If class is not derived from any other class, below would be the chain:
   1. Static Constructor
   2. Instance Constructor
4. If a class is derived from any other class, below would be the chain:
   1. Derived Static Constructor
   2. Base Static Constructor
   3. Base Instance Constructor
   4. Derived Instance Constructor

I hope I have covered all topics related to constructor. Please let me know if I have missed any or if you need more explanation or examples.

!! Happy programming !!

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