Solution to Identifiers

1. simple. Legal but not a good choice -- violates capitalization convention. 
Still have to change filename because Java is case sensitive.

2. SimpleProgram.  Legal and a good choice.

3. 1Simple.  Illegal -- can't start with a digit.

4. _Simple_.  Legal and probably ok, although seems cumbersome compared to Simple.

5. *Simple*.  Illegal -- can't have * in an identifier.

6. $123_45.  Legal but not a good choice -- has nothing to do with the program.

7. Simple!.  Illegal -- can't have ! in an identifier.