That sample and the Java SDK that contains it should be a very good starting point for you. If you have a question about a particular pattern or workflow, and you can't find your answer in the Java SDK, your best bet is to look through the .NET SDK. Any C# sample, walk-through, or snippet should be convertable into Java.
The Network Analyst Java SDK is decidedly less thorough than the .NET SDK. However, there is a Service Area sample available for you to look at:
http://resources.arcgis.com/en/help/arcobjects-java/concepts/engine/#/Solve_service_area/000100000538000000/
That sample and the Java SDK that contains it should be a very good starting point for you. If you have a question about a particular pattern or workflow, and you can't find your answer in the Java SDK, your best bet is to look through the .NET SDK. Any C# sample, walk-through, or snippet should be convertable into Java.
Some excellent resources:
Programming with the ArcGIS Network Analyst Extension
Programming network datasets