I have found Java Sparrows are not too fussy in the type of nest box they use. I have used Budgie nest boxes in the past, and for a couple of years I used the nest boxes, designed for Gouldian Finches, that have an off-set entrance tunnel. I make my own nest boxes and I'm now using a new, deeper, square nest box. Please click on the links below to take you to the pages I have set up that illustrate step-by-step instructions on how to make the nest boxes I use.