// Call this AFTER other action listeners have been registered.
static void addHistoryToTextField(final JTextField input) {
  final Var<Int> historyIdx = new Var(0);
  final new L<S> history;
  input.addKeyListener(new KeyAdapter {
    public void keyPressed(KeyEvent e) {
      if (e.getKeyCode() == KeyEvent.VK_UP) {
        //print("up");
        listSet(history, historyIdx.get(), input.getText(), "");
        historyIdx.set(max(0, historyIdx.get()-1));
        S text = get(history, historyIdx.get());
        if (text != null) {
          input.setText(text);
          input.selectAll();
        }
      }
      
      if (e.getKeyCode() == KeyEvent.VK_DOWN) {
        //print("down");
        S text = input.getText();
        if (historyIdx.get() < l(history) ||
          neq(last(history), text))
          listSet(history, historyIdx.get(), text, "");
        historyIdx.set(min(l(history), historyIdx.get()+1));
        text = get(history, historyIdx.get());
        input.setText(unnull(text));
        input.selectAll();
      }
    }
  });
  
  input.addActionListener(actionListener {
    S text = input.getText();
    //print("Text: " + text);
    while (history.contains("")) history.remove("");
    history.remove(text);
    history.add(text);
    historyIdx.set(l(history));
  });
}