CommandPlugin Interface
The CommandPlugin interfaces provides a very simple void doCommand( String[] args ) method. If you create a command Plugin using just the Interface then you will need to parse the arguments yourself.
ArgsParsingCommandPlugin Helper
If you use the ArgsParsingCommandPlugin abstract class when creating your command plugin you get help when setting up and parsing command arguments. In this case you will uses the Java Simple Argument Parser† by Martian Software and the signature for the command execution method is void doCommand( JSAPResult result ).
In this case the following references will be of use:
† Please note this page suggests the library isn't maintained. However, it was actually last updated on 11 April 2013