private final method

[Saibabaa Pragada]

Hi, How private final makes sense here.. What I mean is, What is the difference between private final and just private?? Subclass cannot see this method in any case.

public class MyClass{
    private final void hello() {
    }
}    

[Sumit Khurana]

final means you can't override this method.

and declaring a method private means it wouldn't be seen by its subclasses.if it is not visible means it can't be overriden.

so,declaring a private method final is redundant.
because declaring a method final means you are saying to compiler don't override this method.but declaring it private also means the same implicitly.

[Stephan van Hulst]

You can still override private methods, if you define an extending class within the same class. Final would in this case prevent the method from being overridden by a subclass within the same class.

The use of this is still questionable though. Private final just doesn't make much sense. I was just pointing out that it's not necessarily redundant.

[Mohamed Sanaulla]

Stephan van Hulst wrote:You can still override private methods, if you define an extending class within the same class. Final would in this case prevent the method from being overridden by a subclass within the same class.

The use of this is still questionable though. Private final just doesn't make much sense. I was just pointing out that it's not necessarily redundant.

I just tried a sample code:

 public class MyClass{  

     public static void main(String[] args){
	     MyClass myC = new MyClass();
	     MySubClass sub = myC.new MySubClass();
	     sub.hello();
	     sub.hello2();
     }
	private final void hello() {  
	     System.out.println("Hello");
    }
    private void hello2()
     {
	     System.out.println("Hello2");
     }
    
	class MySubClass extends MyClass{
	     private void hello2()
	     {
		     System.out.println("Sub Hello2");
	     }
	     private void hello()
	     {
		     System.out.println("Sub Hello");
	     }
     }
 } 

    

Output:

D:\dev\java>javac MyClass.java

D:\dev\java>java MyClass
Sub Hello
Sub Hello2

When I tried to remove the private from the method hello() in MyClass and compile-

D:\dev\java>javac MyClass.java
MyClass.java:22: hello() in MyClass.MySubClass cannot override hello() in MyClas
s; overridden method is final
              void hello()
                   ^
1 error

[bhanu chowdary]

mohammed sanaullah wrote:

Stephan van Hulst wrote:You can still override private methods, if you define an extending class within the same class. Final would in this case prevent the method from being overridden by a subclass within the same class.

The use of this is still questionable though. Private final just doesn't make much sense. I was just pointing out that it's not necessarily redundant.

I just tried a sample code:

 public class MyClass{  

     public static void main(String[] args){
	     MyClass myC = new MyClass();
	     MySubClass sub = myC.new MySubClass();
	     sub.hello();
	     sub.hello2();
     }
	private final void hello() {  
	     System.out.println("Hello");
    }
    private void hello2()
     {
	     System.out.println("Hello2");
     }
    
	class MySubClass extends MyClass{
	     private void hello2()
	     {
		     System.out.println("Sub Hello2");
	     }
	     private void hello()
	     {
		     System.out.println("Sub Hello");
	     }
     }
 } 

    

Output:

D:\dev\java>javac MyClass.java

D:\dev\java>java MyClass
Sub Hello
Sub Hello2

The above code is not overriding. I have changed the code with superclass reference and subclass object.

  public class MyClass{     
	  
    public static void main(String[] args){   
        MyClass myC = new MyClass().new MySubClass();   
        myC.hello();   
        myC.hello2();   
    }   
   private final void hello() {     
        System.out.println("Hello");   
   }   
   private void hello2()   
    {   
        System.out.println("Hello2");   
    }   
      
   class MySubClass extends MyClass{   
        private void hello2()   
        {   
            System.out.println("Sub Hello2");   
        }   
        private void hello()   
        {   
            System.out.println("Sub Hello");   
        }   
    }   
}  

Now the output is Hello
Hello2 which is not the case of overriding.

[Saibabaa Pragada]

Hi Stephan, Your explanation is awesome. Thanks to Mohammed and Bhanu for proving code snippets.

[Stephan van Hulst]

Mohammed and Bhanu, I stand corrected.

Private methods can indeed not be overriden, not even in an internal class. Private final is always redundant.

[Saibabaa Pragada]

Hi Stephan, Earlier you mentioned "You can still override private methods," Here, you said not be overriden. Please confirm the right one. If you think this code is incorrect, Could you Please provide some code on how to use this concept, so that we can understand properly.

Stephan van Hulst wrote:Mohammed and Bhanu, I stand corrected.

Private methods can indeed not be overriden, not even in an internal class. Private final is always redundant.

[Stephan van Hulst]

My last post is the correct one. My view in the first post was corrected by Mohammed and Bhanu.

You asked if there's a difference between private and private final methods. No, there isn't. private final is redundant. Always use private only.

[Sumit Khurana]

On private methods,no overriding rules and no runtime polymorphism rules applies.It is in the explanation of the examlab question.

so,declaring private with final is redundant.