Re: Anonymous inner Classes accessing final variables?

From:

Daniel Pitts <newsgroup.spamfilter@virtualinfinity.net>

Newsgroups:

comp.lang.java.programmer

Date:

Sun, 02 Dec 2007 10:07:48 -0800

Message-ID:

<-6ydnSutVefhac_anZ2dnUVZ_g-dnZ2d@wavecable.com>

getsanjay.sharma@gmail.com wrote:

On Dec 2, 6:55 am, Patricia Shanahan <p...@acm.org> wrote:

The inner class object may still exist long after the method has
completed. The value it sees for local variables is the value they had
when the object was created.

If non-final variables had been permitted, people would have wasted time
debugging obscure run-time failures due to a variable having changed value.

Hello Patricia,

Can you give a real time example on what kind of complexities can
arise if non-final variables were permitted inside inner classes /
anonymous classes?

Thanks and regards,
/~STS

I sure can. Imagine this situation:

public void stuff() {
   String foo = "Hello";
   Runnable r = new Runnable() {
     public void run() {
    while (foo.size() < 1000) {
           foo += ".";
         }
     }
   };
   new Thread(r).start();
   System.out.println(foo);
   foo = null;
   return r;
}

So, what is the behavior of this snippet when someone calls "stuff"? Is
it obvious or did you have to think about it for a while? Imagine that
the runnable returned was used from some other place in this class?
--
Daniel Pitts' Tech Blog: <http://virtualinfinity.net/wordpress/>