It is just a naming convention. No one actually cares, as long as you make sure that there is no other class with the name "comeducambridge.MyClass" in the world.
You can call it with just the name of your company, for example "mycoolcompany", if you totally sure that there is no other "mycoolcompany". Even if there is, unless this company writes java code, you will not have any problems, caused by class name conflicts, when some "lucky" user will manage to use two libraries with the same "mycoolcompany" package prefix.
Using "net.mycoolcompany" for me makes no sense, but maybe if you want to make your domain popular, you should do it.
Just don't call your package prefix "java.util", it is already occupied.