You have to run your application for a long time to see if it's really a memory leak. Keep in mind that garbage collection only occurs periodically, so if you're running a short program you may not see the objects get garbage collected, because the GC just hasn't bothered to do it yet. You can also call System.gc() to manually invoke garbage collection, and then do Thread.sleep for a while.
In Netbeans, try using the VM Telemetry view (under the Profiler tab) to watch the total memory usage. (You can set the profiling mode to "monitor" rather than "memory" or "cpu", which takes much less overhead because it's just keeping track of the VM Telemetry info.) If you run the program for a long time, you should start to see a wave-like pattern where the total memory usage drops at each garbage collection, then slowly builds up, then drops again. However, if the memory usage slowly goes up over time, then you know you've got a memory leak. That's when you should start doing actual memory profiling and see if your char arrays are being persisted rather than garbage collected. It could also be some other data structure you never guessed, so keep track of the "surviving generations" rather than total number. Netbeans has a good tutorial here: http://www.netbeans.org/kb/articles/nb-profiler-uncoveringleaks_pt1.html