IDEs (and obviously DrJava) are programmed to notice readers, writers, etc., which are not closed. If you open a reader pointing to a file and never close it, the file may become inaccessible to other code, we hope temporarily. So they give you a warning, which you can overlook. Try opening and closing a Scanner pointing to System.in and you will find out why you should ignore such warnings whenever System.in System.out and System.err are involved.
What do you have to say for yourself? Hmmm? Anything? And you call yourself a tiny ad.