Java Final

You use the final keyword to mark a variable constant, so that it can be assigned only once. So you must initialize a final variable with a value. If its not initialized (when declared, inside a constructor or inside static blocks), a compile-time error will occur.

Examples

1. PI is now a constant. Any attempt to reassign the value for PI will cause an error.

class MyClass {
  public static final double PI = 3.14;
  public static void main(String[] args){
    System.out.println(PI);
  }
}

2. If you make any method as final, you cannot override it.

class Bike{  
  final void run(){System.out.println("running");}  
}  

class Honda extends Bike{  
   void run(){System.out.println("running safely with 100kmph");}  

   public static void main(String args[]){  
   Honda honda= new Honda();  
   honda.run();  
   }  
}  

The above code execution produces a compile-time error.

3. If you make any class as final, you cannot extend it.

final class Bike{}  

class Honda1 extends Bike{  
  void run(){System.out.println("running safely with 100kmph");}  

  public static void main(String args[]){  
  Honda1 honda= new Honda();  
  honda.run();  
  }  
}

The above code execution also produces a compile-time error.

More Information:

• Oracle Java Docs – final variables