I think you can not have nested packages.
But if you can do the following
In folder \\com there are some classes.
In folder \\com\abc there are some classes.
In folder \\com\abc\xyz there are some classes.
And you want to keep these classes in com,com.abc and com.abc.xyz package respectively.
It can be done easily. Just compile these
java files with corresponding package name
in the corresponding folders and you get a package in a package.
I hope this is what you are looking for.
Girish