Can you show some of your code, especially any reference to a class called "Loop"? The error is saying that java wants to load a class called Loop, but it can't find it in anywhere in the current classpath.
thanks for ur reply
i tried that program in both IDE and command prompt.In command promp its saying that :noclassdeffounderror.
I assume that you are able to run your app with no prob through the IDE. For the CMD, make sure you change the directory to the path where the java class file is logically stored. You should be able to run it now. If you don't want to have to change to different directories to run your apps every single time, then take the advice that has been given to you already, "LEARN ABOUT SETTING THE CLASSPATH ENVIRONMENT VARIABLE!"