code: public static File jarFile(Class<?> clazz) throws IOException {
          return jarFile(classFileUrl(clazz), clazz.getName().replace('.', '/') + ".class");
      }
docs: Locates the jar file that contains the given class.
  <p>
  <p>
  Note that jar files are not always loaded from {@link File},
  so for diagnostics purposes {@link #jarURL(Class)} is preferrable.
  
  @throws IllegalArgumentException
  if failed to determine.