How can I provide word completion functionality in a JComboBox? (When the user enters characters then the closest matching item should be selected)

Alessandro A. Garbagnati

What you are looking for it's some kind of ternary search tree and, you can find a lot of interesting discussions on the net about it.

If you want something ready, you can rely on this JavaWorld article, whose example it's exactly what you are looking for: Plant your data in a ternary search tree