Following Java variable naming conventions is a very important practice. First of all, if you are breaking the rules, then you will be punished with "Invalid Character" compilation error. Secondly, if you are not following the conventions, it will make your variable names confusing or unmeaningful or both to yourself and others who will use your code. We don't want our life difficult by even a micro-unit. You too.
For example, see the following two code snippets that show off the difference.
