public void valueChanged(ListSelectionEvent e) { @SuppressWarnings("unchecked") JList<String> sender = (JList<String>) e.getSource(); if (!sender.isSelectionEmpty()) { if (sender.equals(boxList())) updateTubList(sender.getSelectedValue()); if (sender.equals(machineList())) selectedMachine = sender.getSelectedValue(); if (sender.equals(tubList())) selectedTub = sender.getSelectedValue(); } assignButton().setEnabled(!tubList().isSelectionEmpty() && !machineList().isSelectionEmpty()); }