How can I get an event when the user types a key in the TextField of a JComboBox?

This simply becomes a problem of getting at the textfield of a editable combobox.

if (combo.isEditable()) {
  Component c = combo.getEditor().getEditorComponent();
  if (c instanceof JTextField) {
    JTextField tf = (JTextField) c;
    // now listen for key types or
    // add Document listener to the
    // backing the textfield
  } 
}

• textfield.addKeyListener(...)
• textfield.getDocument().addDocumentListsner(...); // better