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

public class CircleFrame extends JFrame
{
    private CirclePanel circlePanel = new CirclePanel();
    private JButton btnStop = new JButton("Stop");
    private CircleThread circleThread = new CircleThread(circlePanel, true);
    
    public CircleFrame()
    {
        this.setLayout(new BorderLayout());
        this.add(circlePanel, BorderLayout.CENTER);
        this.add(btnStop, BorderLayout.SOUTH);    //貌似我的电脑上North方向也出现了一个JButton，不知道是不是java虚拟机的bug
        
        btnStop.addActionListener(new ActionListener()
            {
                public void actionPerformed(ActionEvent event)
                {
                    if (btnStop.getText().equals("Stop"))
                    {
                        btnStop.setText("Continue");
                        circleThread.setIsCircling(false);
                    }
                    else
                    {
                        btnStop.setText("Stop");
                        circleThread.setIsCircling(true);
                    }
                }
            });
        
        circleThread.start();
    }
    
    public static void main(String[] args)
    {
        EventQueue.invokeLater(new Runnable()
            {
                public void run()
                {
                    JFrame frame = new CircleFrame();
                    frame.pack();
                    frame.setLocationRelativeTo(null);
                    frame.setVisible(true);
                    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                }
            });
    }
}

class CirclePanel extends JPanel
{
    private int startAngle = 0;
    private int arcAngle = 90;    //只有四种颜色，每种颜色占90度
    
    public CirclePanel()
    {
        this.setPreferredSize(new Dimension(400, 400));
    }
    
    public void paintComponent(Graphics g)
    {
        super.paintComponents(g);
        g.setColor(Color.RED);        //这里为了简便，只画了四种颜色
        g.fillArc(100, 100, 200, 200, startAngle, arcAngle);
        g.setColor(Color.YELLOW);
        g.fillArc(100, 100, 200, 200, startAngle + arcAngle, arcAngle);
        g.setColor(Color.BLUE);
        g.fillArc(100, 100, 200, 200, startAngle + arcAngle * 2, arcAngle);
        g.setColor(Color.GREEN);
        g.fillArc(100, 100, 200, 200, startAngle + arcAngle * 3, arcAngle);
    }
    
    public void setStartAngle(int startAngle)
    {
        this.startAngle = startAngle;
    }
}

class CircleThread extends Thread
{
    private CirclePanel circlePanel;
    private boolean isCircling;
    
    public CircleThread(CirclePanel circlePanel, boolean isCircling)
    {
        this.circlePanel = circlePanel;
        this.isCircling = isCircling;
    }
    
    public void setIsCircling(boolean isCircling)
    {
        this.isCircling = isCircling;
    }
    
    public void run()
    {
        for (int i = 0; ; i++)
        {
            while (! isCircling)    //用于暂停旋转的
            {
                try 
                {
                    Thread.sleep(10);
                } 
                catch (InterruptedException e) 
                {
                    e.printStackTrace();
                }
            }
            
            circlePanel.setStartAngle(i % 360);    //设置不同的起始旋转角度
            circlePanel.repaint();
            try 
            {
                Thread.sleep(1);        //这个是旋转每度的间隔时间，如果太小好像动画看上去会不流畅
            }
            catch (InterruptedException e) 
            {
                e.printStackTrace();
            }
        }
    }
}