Most of the concurrent functionality GPars provides to Groovy code is also available from Java. Actors, reactors, agents or dataflow concurrency - these can all be used directly from Java.
To give Java developers a head start, we prepared a gpars-mvn-java-demo-2.0.zip, sample pure Java project that you can grab, extract and experiment with. The maven pom file will show you how to setup necessary dependencies and the included Java classes will give you an immediate insight into the GPars Java API. See our download page for a link to that.
You may also check out the Java API section in the User Guide as well as the many code examples of GPars use.