There will be a zip file classes12.zip in the files you downloaded add that to the classpath , it is better you renamce it as classes12.jar and add to class path
If you have done that check whether you oracle is up, I m bit doubtful about the connection string "oracle:thin:@//localhost:1527/sample" I think you dont need this "//" so it will be oracle:thin:@localhost:1527/sample, but Im not sure anyway I cant try it here as I dont have oracle right now then check the file tnsnames.ora and look for "sample" if everything is there then it has to work buddy
