1. Download this source code and add to your Java project:
http://www.orbital-computer.de/JComboBox/source/AutoCompletion.java
2. Add folowing code to enable autocompletion for your JComboBox:AutoCompletion.enable(yourComboBox);
For further information about JComboBox and AutoCompletion see:
http://www.orbital-computer.de/JComboBox/
https://today.java.net/pub/a/today/2007/07/19/adding-auto-completion-to-swing-comboboxes.html