Final Classes:

If a class is marked as final then no class can inherit any feature from the final class.

Final Variables:

A reference variable declared final can never be reassigned to refer to an different object.

Final Methods:
final modifier prevents a method from being modified in a subclass.

The main purpose of using a class being declared as final is to prevent the class from being sub- classed.

A final variable can be explicitly initialized only once.  

The main intention of making a method final would be that the content of the method should not be changed by any outsider

 Final class declaration:
public final class Demo
{
   // body of class
}


Final variable declaration

class Demo
	{
  final int value= 25;
  // examples of declaring constants:
  public static final int BOXWIDTH = 6;
  static final String TITLE = "Executive";
  
  public void changeValue()
	  {
     value = 30; //will give an error 

  }

The above program will give an error because final variable cannot be changed


The Final Method Declaration


class Demo
	{
    public final void changeSalary(){
       // body of method
    }
}