Java 2 API Specification: [java.sun.com/j2se/1.4.2/docs/api]
The Java Tutorial: [java.sun.com/docs/books/tutorial]
Doug Lea, Concurrent Programming in Java Second Edition. The Java Series. Adison-Wesley. ISBN: 0-201-31009-0
Stanley Rabinowitz and Stan Wagon, A Spigot Algorithm for the Digits of Pi, American Mathematical Monthly, March 1995, 195-203.
Jeremy Gibbons, An Unbounded Spigot Algorithm for the Digits of Pi: [web.comlab.ox.ac.uk/oucl/work/jeremy.gibbons/publications/spigot.pdf]