http://java.sun.com/j2se/1.4/docs/api/java/util/SortedMap.html
You may of course have any number of other public functions which you find useful for your project. [edit: I won't change this so late, but I recommend that you *do not* add extra public functions so that your class stays interchangeable with TreeMap]
As the TA implements this interface with own skiplist he may reduce this requirement by allowing you to skip some of the interface requirements. [edit: see the news group for functions which you may skip] If that happens I still think it would be a very beneficial exercise to implement the entire interface.
The class must be named SkipList.java (note the case) and be located in a package called cmsc420. For a tutorial on packages see:
http://java.sun.com/docs/books/tutorial/java/interpack/