Calling class by it is name

I am currently working on Euler project. There are 600 problems, one problem - one class. I split them on levels: 25 problems in one level. What I need, is that user enter problem number and program create instance class of this problem. Now I use reflection, but maybe there is another way to do it. Also in the every class displays two warnings: class not used, constructor not used. Can you tell me is there another way to do it, so warnings doesn't appear? P.S I solve them in Java