title: Is there a method that calculates a factorial in Java?
body: <p>I didn't find it, yet. Did I miss something? 
  I know a factorial method is a common example program for beginners. But wouldn't it be useful to have a standard implementation for this one to reuse?
  I could use such a method with standard types (Eg. int, long...) and with BigInteger / BigDecimal, too.</p>