iPhone uses Objective C, a programming language that was once dormant but has now sprung to life.
I played with Jim Lysts Processing Zones library which made it easy to get things to work quickly. However, more complicated applications I would recommend MT4j if staying with Java.
@jimihertz you can run Processing programs from inside Java programs. There are some examples of this on the Processing web site and in the Processing books. In particular the example I am referring to is Chapter 11 “Integrating Processing with Java” from the book Visualizing Data by Ben Fry, 2008. The book exists on Safari books online.
An example from another Processing book: