Constructor is a block of code that is similar to the method. A constructor looks like an instance method in java but it is not a method, because it does not have a return type. In other words, constructor and method are different. It is called when an instance of the class (Object)  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.

Constructor has same name as the class and looks like this in a java code.

public class ABC {

   //This is the constructor

   ABC(){

   }

   ..

}

How does a constructor work

To understand the working of constructor, lets take an example. lets say we have a class ABC.
When we create the object of ABC like this:

ABC obj = new ABC()

The new keyword here creates the object of class ABC and invokes the constructor to initialize this newly created object

Types of Constructors

There are two types of constructors in Java:

1. Default constructor (no-arg constructor)
2. Parameterized constructor

A constructor is called "Default Constructor" when it doesn't have any parameter. and it is invoked at the time of Object creation.

Syntax of default constructor:
Classname ( ) { }

Constructor with arguments(or you can say parameters) is known as Parameterized constructor.