Java Graphics - 如何拖放drawString文本

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Point;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.util.Random;

import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingConstants;

public class Main {
  private static final String[] LABEL_STRINGS = { "A", "B", "C", "D", "E", "F",
      "G" };
  static int HEIGHT = 400;
  static int WIDTH = 600;
  static int LBL_WIDTH = 60;
  static int LBL_HEIGHT = 40;
  JPanel mainPanel = new JPanel();
  

  public Main() {
    mainPanel.setPreferredSize(new Dimension(WIDTH, HEIGHT));
    mainPanel.setLayout(null);

    MyMouseAdapter myMouseAdapter = new MyMouseAdapter();
    for (int i = 0; i < LABEL_STRINGS.length; i++) {
      JLabel label = new JLabel(LABEL_STRINGS[i], SwingConstants.CENTER);
      label.setSize(new Dimension(LBL_WIDTH,
          LBL_HEIGHT));
      label.setOpaque(true);
      Random random = new Random();
      label.setLocation(random.nextInt(WIDTH - LBL_WIDTH),
          random.nextInt(HEIGHT - LBL_HEIGHT));
      label.setBackground(new Color(150 + random.nextInt(105), 150 + random
          .nextInt(105), 150 + random.nextInt(105)));
      label.addMouseListener(myMouseAdapter);
      label.addMouseMotionListener(myMouseAdapter);

      mainPanel.add(label);
    }
  }

  public JComponent getMainPanel() {
    return mainPanel;
  }

  public static void main(String[] args) {
    JFrame frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.getContentPane().add(new Main().getMainPanel());
    frame.pack();
    frame.setVisible(true);
  }
}

class MyMouseAdapter extends MouseAdapter {
  private Point initLabelLocation = null;
  private Point initMouseLocationOnScreen = null;

  @Override
  public void mousePressed(MouseEvent e) {
    JLabel label = (JLabel) e.getSource();
    initLabelLocation = label.getLocation();
    initMouseLocationOnScreen = e.getLocationOnScreen();
  }

  @Override
  public void mouseReleased(MouseEvent e) {
    initLabelLocation = null;
    initMouseLocationOnScreen = null;
  }

  @Override
  public void mouseDragged(MouseEvent e) {
    if (initLabelLocation == null || initMouseLocationOnScreen == null) {
      return;
    }
    JLabel label = (JLabel) e.getSource();
    Point mouseLocation = e.getLocationOnScreen();
    int deltaX = mouseLocation.x - initMouseLocationOnScreen.x;
    int deltaY = mouseLocation.y - initMouseLocationOnScreen.y;
    int labelX = initLabelLocation.x + deltaX;
    int labelY = initLabelLocation.y + deltaY;
    label.setLocation(labelX, labelY);
  }
}