Java中JFrame实现无边框无标题方法

package com.qiantu.jframe;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionAdapter;

import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JLayeredPane;
import javax.swing.JPanel;

public class JFrameNoBorder extends JFrame {
 
 public static void main(String[] args) {
 JFrameNoBorder j = new JFrameNoBorder();
 j.setVisible(true);
 }
 
 private static final long serialVersionUID = 1L;
 //用于处理拖动事件，表示鼠标按下时的坐标，相对于JFrame
 int xOld = 0;
 int yOld = 0;
 
 public JFrameNoBorder() {
 this.setLayout(null);

 //处理拖动事件
 this.addMouseListener(new MouseAdapter() {
  @Override
  public void mousePressed(MouseEvent e) {
  xOld = e.getX();
  yOld = e.getY();
  }
 });
 this.addMouseMotionListener(new MouseMotionAdapter() {
  @Override
  public void mouseDragged(MouseEvent e) {
  int xOnScreen = e.getXOnScreen();
  int yOnScreen = e.getYOnScreen();
  int xx = xOnScreen - xOld;
  int yy = yOnScreen - yOld;
  JFrameNoBorder.this.setLocation(xx, yy);
  }
 });

 //JLayeredPane用于添加两个图层的，一个用于背景，一个用于界面
 JLayeredPane layeredPane = new JLayeredPane();
 layeredPane.setBounds(0, 0, 200, 200);
 this.add(layeredPane);
 
 //背景Panel
 JPanel bgPanel = new JPanel();
 bgPanel.setBounds(0, 0, 200, 200);
 layeredPane.add(bgPanel);
 
 //背景图片，添加到背景Panel里面
 JLabel bgLabel = new JLabel(new ImageIcon("img/bgImage.png"));
 bgPanel.add(bgLabel);
 
 //主界面，也就是背景上面的一层Panel
 JPanel mainPanel = new JPanel();
 mainPanel.setBounds(0, 0, 200, 200);
 mainPanel.setLayout(null);
 layeredPane.add(mainPanel);

 //关闭按钮
 JButton closeButton = new JButton();
 closeButton.setIcon(new ImageIcon("img/closeButton.png"));
 closeButton.setBounds(170, 0, 30, 30);
 closeButton.addActionListener(new ActionListener() {
  @Override
  public void actionPerformed(ActionEvent e) {
  System.exit(0);
  }
 });
 mainPanel.add(closeButton);
 
 this.setBounds(50,50,200,200);
 this.setUndecorated(true);
 }
}