Constructor

Constructors have same name as their class. It is different from method. Methods use names other than the class name.
The constructor gets called when we create an object of a class (i.e. new keyword followed by class name). For e.g. Demo obj =  new Demo(); (here Demo() is a default constructor of Demo class).

Default constructor: It is also known as no-arg constructor. Constructor with no arguments is known as default constructor.

Examples:

class Demo
{
     public Demo()
     {
         System.out.println("This is a default constructor");
     }
}

Parameterized constructor: Constructor with argument list is known as parameterized constructor.

class Demo
{
      public Demo(int num, String str)
      {
           System.out.println("This is a parameterized constructor");
      }
}