final Keyword In Java

final is a  keyword which is used in variable, method and class.

final variable

If a variable is declared as final then we cannot change the value, once it is initialized.

In other words the variable is constant

Example:

class DemoFinal{ 

 final int x=50; //final variable 

 void display()

{ 

  x=78; 

  System.out.println("x is:"+x);

 } 

 public static void main(String args[]){ 

  DemoFinal df=new   DemoFinal(); 

 df.display(); 

 } 

}

Output: Compile time error

Note:

It provides compile time error because x is declared as final and the value is 50, again you assign the value of x is 78.So it’s not possible because x is final variable and it acts like a constant .once you assign the value, you cannot change it.

 final method

If a method is declared as final then we cannot write the same method again and again.

In other words final method cannot be overridden.

Note:

final method can be overloaded because you know that overloading is same name and different parameter.

Example:

class DemoFinal{ 

 

final void display(int x){ 

 

  System.out.println("square is:"+(x*x));

 } 

}

 class Result extends DemoFinal

 {

     void display(int x){ 

 

  System.out.println("cube is:"+(x*x*x));

 } 

 public static void main(String args[]){ 

  Result r1=new   Result(); 

 r1.display(7); 

 } 

}

Output:

Compile time error

Note:

It provides compile time error because display method is declared as final and again you repeat same method in child class and you know that final method cannot be overridden

final class

If a class is declared as final then we cannot extends new class from final class.

In other words final class cannot be inherited.

Example:

final class DemoFinal{ 

 

  void display(int x){ 

 

  System.out.println("square is:"+(x*x));

 } 

}

 class Result extends DemoFinal

 {

     void display(int x){ 

     super.display(5)

 

  System.out.println("cube is:"+(x*x*x));

 } 

 public static void main(String args[]){ 

  Result r1=new   Result(); 

 r1.display(6); 

 } 

}

Output:

Compile time error

 Note:

It provides compile time error because DemoFinal class  is declared as final and  you know that final class cannot be inherited.