How Broker pattern could be implemented in Java?

I wonder how the right Java implementation of message Broker looks. Here is exact task desciption:

Message Broker is a system for message exchange. 
There are multiple producers sending messages to multiple consumers.
Then, producer creates message with a topic and the message is delivered to dedicated queue (one queue per topic).
Consumers can subscribe to topics (queues) they like.
Each consumer gets messages from topics he subscribed to. 
Multiple consumers can subscribe to one topic.
The design should use multi threading and prevent thread starvation.

I am curious to see a good design example: which classes should be defined, how these classes interact?

Thank you!