Final Keyword In Java

Final keyword can be used with variables, methods and class.

Final Keyword

final variables

• final variables are nothing but constants. We cannot change the value of a final variable once it is initialized.
• It is a good practice to name final variable in all CAPS.
• Local final variable must be initialized during declaration.
• A final variable that have no value at the time of declaration it is called blank final variable or uninitialized final variable. It can be initialized in the constructor only.
• The blank final variable can be static also which will be initialized in the static block only.

Example - Modifying final variable gives Compile Time Error

class Car {  
  final int speedLimit=90;//final variable  
  void run() {  
    speedLimit=400;  //Error: You cannot modify final variable
  }  
  public static void main(String args[]){  
    Car obj = new  Car();  
    obj.run();  
  }  
}

Example - For initializing blank final variable

class Sample {  
    final int MAX_VALUE;	//Blank final variable	 
    Sample() {
        MAX_VALUE=100;	//It must be initialized in constructor
    }
    void myMethod(){  
        System.out.println(MAX_VALUE);
    }  
    public static void main(String args[]){  
        Sample obj = new  Sample();  
        obj.myMethod();  
    }  
}

final method

A final method cannot be overridden. Which means even though a subclass can call the final method of parent class without any issues but it cannot override it. Example - You cannot override method. You will get compile time error.

class Sample {  
    final void demo() {
      System.out.println("Sample Class Method");
    }  
}  
	     
class ABC extends Sample {  
    void demo() {
        System.out.println("ABC Class Method");
    }  
	     
    public static void main(String args[]){  
        ABC obj = new ABC();  
        obj.demo();  
    }  
}

Example - You can inherit method but cannot override.

class Sample {  
   final void demo() {
      System.out.println("Sample Class Method");
   }  
}  
	     
class ABC extends Sample {  
   public static void main(String args[]){  
      ABC obj = new ABC();  
      obj.demo();  
   }  
}

final class

We cannot extend a final class. If you make any class as final, you cannot extend it. Example - You will get Compile Time Error

final class Sample{  
}  
	     
class ABC extends Sample{  
   void demo(){
      System.out.println(“Demo Method");
   }  
   public static void main(String args[]){  
      ABC obj= new ABC(); 
      obj.demo();
   }  
}

Note

• A constructor cannot be declared as final. Because constructor is never inherited.
• All variables declared in an interface are by default final.
• If method parameters are declared final then the value of these parameters cannot be changed.