javah -help prints this:

Usage:
  javah [options] <classes>
where [options] include:
  -o <file> Output file (only one of -d or -o may be used)
  -d <dir> Output directory
  -v -verbose Enable verbose output
main.opt.h <<<===what's this?
  -version Print version information
  -jni Generate JNI-style header file (default)
  -force Always write output files
  -classpath <path> Path from which to load classes
  -bootclasspath <path> Path from which to load bootstrap classes
<classes> are specified with their fully qualified names
(for example, java.lang.Object).