Constructors in Java

In Java, a constructor is a block of codes similar to the method. It is called when an instance of the class is created. At the time of calling constructor, memory for the object is allocated in the memory.

It is a special type of method which is used to initialize the object.

Every time an object is created using the new() keyword, at least one constructor is called.

It calls a default constructor if there is no constructor available in the class. In such case, Java compiler provides a default constructor by default.

There are two types of constructors in Java: no-arg constructor, and parameterized constructor.

Note: It is called constructor because it constructs the values at the time of object creation. It is not necessary to write a constructor for a class. It is because java compiler creates a default constructor if your class doesn’t have any.

Rules for creating Java constructor

There are two rules defined for the constructor.

1. Constructor name must be the same as its class name
2. A Constructor must have no explicit return type
3. A Java constructor cannot be abstract, static, final, and synchronized
   Types of Java constructorsThere are two types of constructors in Java:
   1. Default constructor (no-arg constructor)
   2. Parameterized constructor

1) Java Default Constructor

A constructor is called “Default Constructor” when it doesn’t have any parameter

Example of default constructor

class Defaultconstructor

{

Defaultconstructor()
{
System.out.println(“Constructor is created”);

}

public static void main(String args[])

{
Defaultconstructor b=new Defaultconstructor();
}
}

2)Java Parameterized Constructor

A constructor which has a specific number of parameters is called a parameterized constructor.

Why use the parameterized constructor?

The parameterized constructor is used to provide different values to distinct objects. However, you can provide the same values also.

Example of parameterized constructor

In this example, we have created the constructor of Student class that have two parameters. We can have any number of parameters in the constructor.

class Paraconstructor
{
int id;
String name;

Paraconstructor(int i,String n)
{
id = i;
name = n;
}
void display(){System.out.println(id+” “+name);}

public static void main(String args[]){
Paraconstructor s1 = new Paraconstructor(111,”Karan”);
Paraconstructor s2 = new Paraconstructor(222,”Aryan”);
s1.display();
s2.display();
}
}

Difference between constructor and method in Java

There are many differences between constructors and methods. They are given below.

Java Constructor	Java Method
A constructor is used to initialize the state of an object.	A method is used to expose the behavior of an object.
A constructor must not have a return type.	A method must have a return type.
The constructor is invoked implicitly.	The method is invoked explicitly.
The Java compiler provides a default constructor if you don’t have any constructor in a class.	The method is not provided by the compiler in any case.
The constructor name must be same as the class name.	The method name may or may not be same as the class name.