Richard,
Here are links to photos of Duhat and Java Plum:
http://www.stuartxchange.org/Duhat.jpg
http://www.tradewindsfruit.com/java_plum5.jpg
UF/IFAS Okeechobee Extension Service - Java Plum or Jambolan
It is possible that what you have tasted is the June Plum or the Ambarella (Spondias Chyteria, Spondias Dulcis):
http://www.tntisland.com/images/juneplum.jpg. It is similar and related to the Hog Plum (Spondias Mombin), but is much bigger than the latter. They both have single seeds, but the Hog Plum has a round seed section while the June Plum has star shaped seed section, as the photo shows. Hre's a photo of a Hog Plum seed:
http://www.seabean.com/guide/Spondia...ias_mombin.jpg