Why we are making a variable as final in method inner class ?

Question

Why we are making the variable as final (method inner class) while we are accessing the method variable in inner class ?
regards,
namanc

Answer 1

As far as I can tell, the only reason is to protect the programmer: when the inner class instance is constructed, it is given the then-current value of the variable. If the variable (or method parameter) later changes, the value held by the inner class would not. By making the variable final, the programmer doesn't have to worry about them staying in sync.
Here's some code to ponder:
public class InnerExample
    void printMe( final int x )
        Runnable runMe = new Runnable()
            public void run()
                System.out.println(x);
        (new Thread(runMe)).start();
}When compiled with the Sun JDK 1.4.2, you get this bytecode:
void printMe(int);
  Code:
   0:   new     #2; //class InnerExample$1
   3:   dup
   4:   aload_0
   5:   iload_1
   6:   invokespecial   #3; //Method InnerExample$1."<init>":(LInnerExample;I)V
   9:   astore_2
   10:  new     #4; //class Thread
   13:  dup
   14:  aload_2
   15:  invokespecial   #5; //Method java/lang/Thread."<init>":(Ljava/lang/Runnable;)V
   18:  invokevirtual   #6; //Method java/lang/Thread.start:()V
   21:  returnAt line (byte) 5, it loads the passed value onto the stack; at line 6, it invokes the inner class constructor (which is created by the compiler). Nothing in this sequence of code would prevent use of a non-final variable.