JavaSwing中随意拖动组件的位置

在很多地方都看到有人问怎么拖动组件的位置，其实非常简单，就是鼠标监听加一个算法而已，代码承上。

import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.EventQueue;
import java.awt.Color;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;

import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JPanel;


public class DraggedTest extends JFrame {

	private JPanel contentPane;

	public static void main(String[] args) {
		EventQueue.invokeLater(new Runnable() {
			public void run() {
				try {
					DraggedTest frame = new DraggedTest();
					frame.setVisible(true);
				} catch (Exception e) {
					e.printStackTrace();
				}
			}
		});
	}

	public DraggedTest() {
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		setSize(660, 500);
		setLocationRelativeTo(null);
		contentPane = new JPanel();
		contentPane.setLayout(new BorderLayout());
		add(contentPane);
		
		JPanel panel = new JPanel();
		contentPane.add(panel, BorderLayout.CENTER);
		panel.setBorder(BorderFactory.createLineBorder(Color.orange, 2));
		panel.setLayout(null);
		
		JPanel panel_1 = new JPanel();
		panel_1.setBackground(Color.GRAY);
		panel_1.setBounds(82, 85, 130, 130);
		panel.add(panel_1);
		
		JPanel panel_2 = new JPanel();
		panel_2.setBackground(Color.LIGHT_GRAY);
		panel_2.setBounds(261, 85, 130, 130);
		panel.add(panel_2);
		
		JPanel panel_3 = new JPanel();
		panel_3.setBackground(Color.MAGENTA);
		panel_3.setBounds(450, 85, 130, 130);
		panel.add(panel_3);
		
		JPanel panel_4 = new JPanel();
		panel_4.setBackground(Color.ORANGE);
		panel_4.setBounds(261, 285, 130, 130);
		panel.add(panel_4);
		
		MyListener m = new MyListener();
		panel_1.addMouseListener(m);
		panel_1.addMouseMotionListener(m);
		
		panel_2.addMouseListener(m);
		panel_2.addMouseMotionListener(m);
		
		panel_3.addMouseListener(m);
		panel_3.addMouseMotionListener(m);
		
		panel_4.addMouseListener(m);
		panel_4.addMouseMotionListener(m);
	}
	// 写一个类继承鼠标监听器的适配器，这样就可以免掉不用的方法。
	class MyListener extends MouseAdapter{
		//这两组x和y为鼠标点下时在屏幕的位置和拖动时所在的位置
		int newX,newY,oldX,oldY;
		//这两个坐标为组件当前的坐标
		int startX,startY;
	
		@Override
		public void mousePressed(MouseEvent e) {
			//此为得到事件源组件
			Component cp = (Component)e.getSource();
			//当鼠标点下的时候记录组件当前的坐标与鼠标当前在屏幕的位置
			startX = cp.getX();
			startY = cp.getY();
			oldX = e.getXOnScreen();
			oldY = e.getYOnScreen();
		}
		@Override
		public void mouseDragged(MouseEvent e) {
			Component cp = (Component)e.getSource();
			//拖动的时候记录新坐标
			newX = e.getXOnScreen();
			newY = e.getYOnScreen();
			//设置bounds,将点下时记录的组件开始坐标与鼠标拖动的距离相加
			cp.setBounds(startX+(newX - oldX), startY+(newY - oldY), cp.getWidth(), cp.getHeight());
		}

	}
}