Java Swing - 如何在点击之前处理JComboBox下拉列表更改侦听器

import java.awt.Component;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;

import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JList;
import javax.swing.plaf.basic.BasicComboBoxRenderer;

public class Main {
  JComboBox combo = new JComboBox();
  public Main() {
    combo.setRenderer(new ComboToolTipRenderer(combo));
    combo.addItemListener(e -> System.out.println(combo.getSelectedItem().toString()));
    combo.addItem("");
    combo.addItem("Long text 4");
    combo.addItem("Long text 3");
    combo.addItem("Long text 2");
    combo.addItem("Long text 1");
    JFrame f = new JFrame();
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    f.add(combo);
    f.pack();
    f.setVisible(true);
  }
  public static void main(String[] args) {
    new Main();
  }
}

class ComboToolTipRenderer extends BasicComboBoxRenderer {
  static final long serialVersionUID = 1L;
  JComboBox combo;
  JList comboList;
  ComboToolTipRenderer(JComboBox combo) {
    this.combo = combo;
  }

  @Override
  public Component getListCellRendererComponent(JList list, Object value,
      int index, boolean isSelected, boolean cellHasFocus) {
    super.getListCellRendererComponent(list, value, index, isSelected,
        cellHasFocus);
    if (comboList == null) {
      comboList = list;
      KeyAdapter listener = new KeyAdapter() {

        @Override
        public void keyReleased(KeyEvent e) {
          if (e.getKeyCode() == KeyEvent.VK_DOWN
              || e.getKeyCode() == KeyEvent.VK_UP) {
            int x = 5;
            int y = comboList.indexToLocation(comboList.getSelectedIndex()).y;
            System.out.println(comboList.getSelectedIndex());
          }
        }
      };
      combo.addKeyListener(listener);
      combo.getEditor().getEditorComponent().addKeyListener(listener);
    }
    if (isSelected) {
      System.out.println(value.toString());
    }
    return this;
  }
}