Final Keyword

A final keyword has a numerous way to use. 

A final class cannot be subclassed. 

A final method cannot be overridden by sub classes. 

A final variable can apply only be initialized once.

Example:-
public Class Hello
{
public final int number;
{
Hello() //Use a constructor
{
number=10;
}
}

---

Public Class MyClass
{
public static void main(string[] args)
{
Hello hel=new Hello();    //Use a Hello Class
hel.number=20;
}
}