let's play TDD, tackles closures in java

[Tom Hawtin]

On 20/12/2010 10:42, Brian Goetz wrote:
>> The long, special-purpose way around, using anonymous inner classes (or
>> local classes), is actually rather easy.
>>
>>      new XyzListener() {
>>          private boolean fired;
>>          public void event(XyzEvent event) {
>>              fired = true;
>>          }
>>          {
>>              abc.addXyzListener(this);
>>              abc.doThing();
>>              assertTrue(fired);
>>          }
>>      }
>
> Yuck.  Not only does it use the hard-to-read instance initializer feature, but it allows the 'this' reference to escape during construction, which is a no-no.

It's going to be a compromise in the battle against Java's generally 
verbose syntax. The instance initialiser in a tiny anonymous inner class 
looks fine to me. In this case, I don't care that `this` escapes the 
instance initialiser to the enclosing method.

If actual Java wasn't so verbose, what I'd like to write is something like:

     declare listener = new XyzListener() {
         private boolean fired;
         public void event(XyzEvent event) {
             fired = true;
         }
     };
     abc.addXyzListener(listener);
     abc.doThing();
     assertTrue(listener.fired);

The previous code was what is necessary and sufficient to translate this 
into reasonable, real code.

What I believe should be avoided is a lurch away from OO with the 
listener data being split from the listener into the enclosing context.

Of course, you don't want to repeat this sort of code for every single 
possible `doThing(args)`.

Tom