In your experience, what is a useful rule of thumb for how many lines of code are too many for one class in Java?
To be clear, I know that number of lines is not even close to the real standard to use for what should be in a particular class and what shouldn't. Classes should be designed according to proper OOP philosophies (encapsulation, etc.) in mind. That said, a rule of thumb could provide a useful starting point for refactoring considerations (i.e. "Hmmm, this class has >n lines of code; it's probably unreadable and doing a lousy job of encapsulation, so I might want to see if it should be refactored at some point").
On the flip side, perhaps have you encountered examples of very large classes that still obeyed OOP design well and were readable and maintainable despite their length?
Here's a related, non-duplicate question about lines per function.