Implementation Of Constructor in Java

What is constructor?

A constructor is a special type of method of a class that initializes the object of that type. It is an instance method that usually has the same name as the class.

Important points about constructors:

  1. It has no return type.
  2. It is called through the new keyword.
  3. A constructor has the same name as the class.
  4. Generally public or default.

For example:

  1. class mp
    {  
  2.    Mp()
       {  //constructor for class mp  
  3.    }  

Types of constructor

There are basically two types of constructor as given below:

  1. Default constructor
  2. Parameterized constructor

1. Default Constructor

A "default constructor" refers to a null constructor that is automatically generated by the compiler if no constructors have been defined for the class.

A programmer-defined constructor that takes no parameters is also called a default constructor.

For example:

  1. class mp
    {  
  2.     mp()
        {  
  3.        System.out.println(“znl”);  
  4.     }  

2. Parameterized Constructor

It is a type of constructor that requires the passing of parameters on creation of the object.

For example:

  1. class mp
    {  
  2.     mp(int x)
        {  
  3.        System.out.println(“xml”);  
  4.     }  

Constructor Overloading

In Java, a constructor can also be overloaded as a feature of object oriented programming.

Whenever multiple constructors are needed, they are implemented as overloaded methods. It allows more than one constructor inside the class with a different signature.

  1. class mp
    {  
  2.     mp()
        {  
  3.        System.out.println("yahoo");  
  4.     }  
  5.     mp(int a)
        {  
  6.         System.out.println("you have just selected constructor with integer value: "+a);  
  7.     }  
  8.     mp(float a)
        {  
  9.         System.out.println("you have just selected constructor with float value: "+a);  
  10.     }  
  11.     mp(int a, int b)
        {  
  12.         System.out.println("you have just selected constructor with integer values: "+a+" and "+b);  
  13.     }  
  14.     mp(int a, float b)
        {  
  15.        System.out.println("you have just selected constructor with integer value: "+a+" and float value: "+b);  
  16.     }  
  17. }   
  18. class sp
    {  
  19.     public static void main(String []ab)
        {  
  20.         mp a1=new mp();  
  21.         new mp(3);  
  22.         new mp(3,2);  
  23.         new mp(3.3f);  
  24.         new mp(4,8.9f);  
  25.     }  

Output

Output