Possible Duplicate:
Java Naming Convention with Acronyms
Is it getXml() or getXML()? Is there any official Sun/Oracle document on this?
Both are correct. Use your preferred way, and be consistent with it throughout your code.
Except for variables, all instance, class, and class constants are in mixed case with a lowercase first letter. Internal words start with capital letters. Variable names should not start with underscore _ or dollar sign $ characters, even though both are allowed.
来源：https://stackoverflow.com/questions/5704737/java-naming-convention-with-acronyms