I have just created a file in java using an online compiler at http://wwww.compileonline.com but I can't see the file created. Anyone who has used this compiler before please help..
I don't think that compileonline is actually intended to be used as a tool for creating bytecode files. It is primarily a learning tool.
If you want to do serious development and/or produce bytecode files, you are better off downloading and installing a Java JDK distribution and/or a Java IDE.
FWIW, if the site did offer a bytecode creation service, you'd need to think twice about using it. How would you know their compiler doesn't add sneaky stuff to the generated code? How would you know it doesn't save a copy of your code for some reason?
(I'm not implying that they would do these things, but you'd be wise to consider the risk ...)