class Circle
{
              int radius;
              double Area()
              {
                            return Math.PI*radius*radius;
              }
}

Circle c;
c = new Circle();

// When you use new keyword to create an object, the runtime has to construct that object by using the definition of the class. A constructor is a special method that runs automatically when you create an instance of a class.

What is a constructor
What is instance of a class