去掉标题栏的JFrame如何实现拖动

无边框无标题之后是不能拖动了，要自己实现。

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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 extendsJFrame {

  

 publicstatic void main(String[] args) {

 JFrameNoBorder j =new JFrameNoBorder();

 j.setVisible(true);

 }

  

 privatestatic 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

 intxOld = 0;

 intyOld = 0;

  

 publicJFrameNoBorder() {

 this.setLayout(null);

 

 //处理拖动事件

 this.addMouseListener(newMouseAdapter() {

  @Override

  publicvoid mousePressed(MouseEvent e) {

  xOld = e.getX();

  yOld = e.getY();

  }

 });

 this.addMouseMotionListener(newMouseMotionAdapter() {

  @Override

  publicvoid mouseDragged(MouseEvent e) {

  intxOnScreen = e.getXOnScreen();

  intyOnScreen = e.getYOnScreen();

  intxx = xOnScreen - xOld;

  intyy = 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(newImageIcon("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(newImageIcon("img/closeButton.png"));

 closeButton.setBounds(170,0, 30,30);

 closeButton.addActionListener(newActionListener() {

  @Override

  publicvoid actionPerformed(ActionEvent e) {

  System.exit(0);

  }

 });

 mainPanel.add(closeButton);

  

 this.setBounds(50,50,200,200);

 this.setUndecorated(true);

 }

}