Using underscores in Java variables and method names

Rules:

1. Do what the code you are editing does
2. If #1 doesn't apply, use camelCase, no underscores

I don't think using _ or m_ to indicate member variables is bad in Java or any other language. In my opinion, it improves readability of your code because it allows you to look at a snippet and quickly identify out all of the member variables from locals.

You can also achieve this by forcing users to prepend instance variables with "this", but I find this slightly draconian. In many ways it violates DRY because it's an instance variable. Why qualify it twice?

My own personal style is to use m_ instead of _. The reason being that there are also global and static variables. The advantage to m_/_ is it distinguishes a variable's scope. So you can't reuse _ for global or static and instead I choose g_ and s_ respectively.

It's a blend of coding styles. One school of thought is to preface private members with an underscore to distinguish them.

setBar( int bar)
{
   _bar = bar;
}

instead of

setBar( int bar)
{
   this.bar = bar;
}

Others will use underscores to indicate a temporary local variable that will go out of scope at the end of the method call. (I find this pretty useless - a good method shouldn't be that long, and the declaration is right there! So I know it goes out of scope.) God forbid a programmer from this school and a programmer from the memberData school collaborate! It would be hell.

Sometimes, generated code will preface variables with _ or __. The idea being that no human would ever do this, so it's safe.