There are a few standard approaches to asynchrony. Callback is one of
them, Poll Objects (or Futures) are another one. In this design the
async method immediately returns a 'proxy' that will receive the
result as soon as it is available, i.e., the proxy can be 'polled' for
the result.

Ultimately, Poll Objects are only a wrappers for callbacks, but
sometimes this design is simmpler to handle and easier to understand
for the client.

/philipp

There are a few ways to handle this.
Callback is probably the best approach, however you can also use
Executor and other java.util.concurrent classes.

I suggest reading the book Java Concurrency In Practice.  Its been very
useful to me in my exploration of Java concurrency.

<http://virtualinfinity.net/wordpress/technical-book-recommendations/java-concurr
ency-in-practice/>

Good luck,
Daniel.