Constrctor and Its Types

What is  constructor ?

A special method of the class that will be automatically invoked when an instance of the class is created is called as constructor. 

Some of the key points regarding the Constructor are 
  • A class can have any number of constructors.
  • A constructor doesn't have any return type even void.
  • A static constructor can not be a parameterized constructor.
  • Within a class you can create only one static constructor. 

Constructors can be divided into 5 types
  1. Default Constructor
  2. Parameterized Constructor
  3. Copy Constructor
  4. Static Constructor
  5. Private Constructor 

Default Constructor

A constructor without any parameters is called as default constructor. Drawback of default constructor is every instance of the class will be initialized to same values and it is not possible to initialize each instance of the class to different values.

Parametrized Constructor 

A constructor with at least one parameter is called as parametrized constructor. Advantage of parametrized constructor is you can initialize each instance of the class to different values.

Copy Constructor

A parametrized constructor that contains a parameter of same class type is called as copy constructor. Main purpose of copy constructor is to initialize new instance to the values of an existing instance.

Static Constructor

You can create a constructor as static and when a constructor is created as static, it will be invoked only once for any number of instances of the class and it is during the creation of first instance of the class or the first reference to a static member in the class. Static constructor is used to initialize static fields of the class and to write the code that needs to be executed only once.

Private Constructor 

You can also create a constructor as private. When a class contains at least one private constructor, then it is not possible to create an instance for the class. Private constructor is used to restrict the class from being instantiated when it contains every member as static.


I hope this small blog is useful for all readers for interview purposes and understanding the concept about the constructor,if you have any suggestion then please contact me.