Java中如何写代码实现无标题无边框的窗体能够用鼠标拖动改变窗口大小

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;

public class DragFrame extends JFrame {
	private boolean startDrag = false;
	private Point p = null;

	public static void main(String[] args) {
		DragFrame df = new DragFrame();
		df.setUndecorated(true);
		df.setSize(400, 400);
		df.setVisible(true);
	}

	public DragFrame() {
		addMouseListener(new MouseAdapter() {
			public void mousePressed(MouseEvent e) {
				startDrag = true;
				p = e.getPoint();
			}

			public void mouseReleased(MouseEvent e) {
				startDrag = false;
			}
		});
		addMouseMotionListener(new MouseMotionAdapter() {
			public void mouseDragged(MouseEvent e) {
				Point p1 = e.getPoint();
				Point p2 = getLocation(null);
				p2.x += p1.x - p.x;
				p2.y += p1.y - p.y;
				setLocation(p2);
			}
		});
	}
}