Question

I like to know do we synchronize the instance variable which are final. As variables are final there can not be change in the value.
Can anybody explain this?

Answer 1

Do we synchronize instance variables which are final?

Yes. You still have to synchronize mutable objects

final != immutable

 public class Something {
     private final List list = new ArrayList();

     public void add( String value ) {
         this.list.add( value );
     }
     public int count() {
          return this.list.size();
     }
 }

Later

 Something s = new Something();

 Thread a = new Thread() {
    public void run(){
       s.add( "s" );
       s.add( "s" );
       s.add( "s" );
     }
 };
 Thread b = new Thread(){
     public void run() {
         s.count();
         s.count();
     }
 };

 a.start();
 b.start();

If yes then whats the use?

You’re declaring, that a given attribute can’t be changed during the object life time.

This increases the security ( your object attribute can’t be replaced by a malicious subclass )
Allows compiler optimizations ( because it knows that only a reference will be used ever )
Prevents subclasses from changing it and so on.

An attribute that is both, final and immutable ( like String, Integer and others ) doesn’t need synchronization.

class X {
    private final String name = "Oscar";

    public int nameCount(){
        return this.name.length(); //<-- Will return 5 ALWAYS ( actually the compiler might inline it 
    }
 }