The process is called de- compilation. I am attaching a tool here which is
pretty good. It is a utility called JAD. You have to run it like this: jad
<class-file-name.class> It will create a file  called <class-file-name.jad> You
can rename it to <class-file-name.java> However, the variable names that you
give (object names or string names) are not converted as they are, but the tool
converts the names into something that it can. e.g. if your variable name is Car
oMFCar, it might write it like Car car. Still, it is a pretty good tool. It is
possible because, the sun has openly declared structure of class  files in it's
specification. So anybody can decompile the class file if one has access to
them.