Legal Identifiers: 1. must start with a letter, a currency character($), or a connecting character such as the underscore. 2. after the first character, identifiers can contain any combination of letters, currency characters, connecting characters or numbers.
The exam watch says that the rules for legal identifiers are not only for variable names but for ALL java components including methods and classes.
We really, really discourage using an IDE while studying for the SCJP. It's too easy for an IDE to "help" you without telling you, and then you can be left with a misunderstanding about what the compiler or JVM is really doing.
I can tell you for sure that when we create the exam, the entire exam team, crammed into a conference room, is creating every last question using only the command line. Every question is written and tested from the command line. Same goes for all the code and questions in the book.
Spot false dilemmas now, ask me how!
(If you're not on the edge, you're taking up too much room.)