Conditional breakpoints are my new best friends.

Intellij's IDEA has a wonderful feature I discovered the other day: conditional breakpoints. Because the applications I write tend to operate on large amounts of data, the bugs I tend to see are the sort that show up once every thousand or so iterations through some loop. Often the defect is the result of not totally bomb-proofing the application to deal with dirty data. We tend to stream data around, so we don't get nice Lists--often we just get Iterators or Iterables, and for performance reasons, we often don't impose any reproducible order on these collections (so we tend not to use Comparators and my favorite interview question whose answer is LinkedHashMap).

The result is that you can't just pause at position 3721 in the List. You have to wait for the chunk of data that has exactly the structure you're looking for. Enter conditional breakpoints: right-click the breakpoint, go to properties, click on "Condition". What's really great is that the expression box is itself a fully featured mini-IDE, so you get autocomplete goodness. Sweet!