Every robot needs a drive class. What does this mean? A drive class basically mediates between the Navigation System and the commands that are sent to the robot. This is the structure:

Every drive must implement the move() method. From the navigation system it receives:

In the FourWheelHolonomicDrive you can see an implementation of such a method. It sends the commands to a FourWheelHolonomicPort port (a robot that is actually has the required wheels)