Hi Wei,
Pam's explanation is correct. A source file is the .java file.
If you don't mind a suggestion ... if you are studying for the SCJP2 Exam it's better to write and compile your code from the command-line vs using an
IDE. Most IDE's add or optimize code; possibly correcting syntax errors, etc for you. You really need to see how the pure Java compiler handles things.
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Jane Griscti
Sun Certified Programmer for the Java� 2 Platform