Java Swing - 如何获取组件

import java.awt.Component;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;

import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class Main {

  public static void main(String[] args) {
    JComboBox combo = new JComboBox();
    combo.setEditable(true);
    for (int i = 0; i < 10; i++) {
      combo.addItem(i);
    }
    JLabel tip = new JLabel();
    tip.setText("Outside combobox");
    JPanel panel = new JPanel();
    panel.add(combo);
    panel.add(tip);
    panel.addMouseListener(new MouseAdapter() {
      @Override
      public void mouseEntered(MouseEvent e) {
        tip.setText("Outside combobox");
      }
      @Override
      public void mouseExited(MouseEvent e) {
        Component c = SwingUtilities.getDeepestComponentAt(e.getComponent(),
            e.getX(), e.getY());
        tip.setText(c != null && SwingUtilities.isDescendingFrom(c, combo) ? "Inside combo box"
            : "Outside combobox");
      }
    });
    JFrame frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
    frame.add(panel);
    frame.pack();
    frame.setVisible(true);
  }
}