Nested commands. This example allows for /hello if you register Commands.class and allows for /myplugin hello if you register ParentCommand.class

NestedCommandDemo.java

public class Commands {
  public static class ParentCommand {
  	@Command(aliases = { "myplugin"}, desc = "All MyPlugin commands", min = 0, max = -1)
	@NestedCommand(Command.class) //All commands will get passed on to Commands.class
	public static void myplugin(final CommandContext args, CommandSender sender) throws CommandException {
	}
  }  
  @Command(aliases = { "hello", "hey" }, desc = "Says hello", usage = "[player] - The player to say hello to", min = 1, max = 1)
  public static void hello(final CommandContext args, CommandSender sender) throws CommandException {
      Player target = Bukkit.getPlayer(args.getString(0)); //0 is the index
      if (target == null) throw new CommandException("Player "+args.getString(0)+" not found!");
      target.sendMessage("Hello!");
  }
}