Check Rodey Green's
Java Glossary
entry on javac - under the table of command line switches he gives a usage example.
This class is in JAVA_HOME/lib/tools.jar, so you have to include that in CLASSPATH to use it from a program.
As I recall, the main() method is used from javac.exe, but it does a System.exit() - so you don't want to do that from your program. Use the compile() method which returns a boolean for success/fail.