Constructor in Java

Constructor is a special type of method that automatically calls when an object is created. Constructors are mainly used to initialize objects. We can also initialize an object with the help of methods, for example setData(). 

Rules for Creating Constructor

- Constructors have the same name as the class itself.

- Constructor has not any return type, even void.

- Constructors can have access modifier.

Types of Constructor in Java

There are two types of constructor in java.

Java No-Argument Constructor

A constructor that has no parameter is known as no-argument constructor. No-argument constructor is also known as default constructor. If we don't create any type constructor in a class, then compiler automatically creates default constructor. But if we define any type of constructor, then compiler does not create any constructor. Compiler created constructor initialize an object to the default value, depends on its data members. 

Example of Java No-Argument Constructor

class Testing 
{
 String name;
 int id;

 Testing()
 {
  System.out.println("A default constructor has no parameter");
 }
}
class DefConstructor
{
 public static void main(String[] args) {
  Testing t = new Testing();
 }
}

Output:

A default constructor has no parameter

Java Parameterized Constructor

A constructor that has parameters is known as parameterized constructor. A parameterized constructor can have one or more parameters. 

Example of Java Parameterized Constructor

class Testing 
{
 String name;
 int id;

 Testing(int x, String n)
 {
  id = x;
  name = n;
 }
 void showData()
 {
  System.out.println("Id : "+id+"\nName : "+name);
 }
}
class DefConstructor
{
 public static void main(String[] args) {
  Testing t = new Testing(1, "Bill");
  t.showData();
 }
}

Output:

Id : 1
Name : Bill

Constructor Overloading in Java

A class can have any number of constructors. Compiler differentiates constructors by number of parameters and type of parameters and order of constructors in which they are defined.

Example of Constructor Overloading in Java

class ConOverloading
{
 ConOverloading()
 {
  System.out.println("Default constructor is running");
 }
 ConOverloading(int x)
 {
  System.out.println("Parameterized constructor is running");
 }
 ConOverloading(ConOverloading c)
 {
  System.out.println("Copy constructor is running");
 }
 public static void main(String[] args) {
  ConOverloading c1 = new ConOverloading();
  ConOverloading c2 = new ConOverloading(10);
  ConOverloading c3 = new ConOverloading(c1);
 }
}

Output:

Default constructor is running
Parameterized constructor is running
Copy constructor is running