跟着音乐节奏随机的产生不同颜色形状的图形

import javax.sound.midi.*;
import javax.swing.*;

public class miniplayer1{
    Panel panel;
    JFrame frame;
    public  MidiEvent  MakeEvent(int comd,int chan,int note,int vol,int tick){
        MidiEvent event;
        event = null;
        try{
            ShortMessage a = new ShortMessage();
            a.setMessage(comd, chan, note, vol);
            event = new MidiEvent(a,tick);
        }catch(Exception ex){}
        
        return event;
    }
    
    public void setGui(){
        frame = new JFrame("My music App");
        panel = new Panel();
        
        frame.getContentPane().add(panel);
        frame.setBounds(100, 100, 200, 200);
        frame.setVisible(true);
    }
    public void go(){
        setGui();
        try{
            Sequencer sequencer = MidiSystem.getSequencer();
            sequencer.open();
            
            int [] eventIwant = {127};
            sequencer.addControllerEventListener(panel,eventIwant);
            Sequence seq = new Sequence(Sequence.PPQ,4);
            Track track = seq.createTrack();
            
            for(int i = 5; i < 200; i += 4){
                int r = (int)(Math.random() * 50) + 1;
                track.add(MakeEvent(144,1,r,100,i));
                track.add(MakeEvent(176,1,127,0,i));
                track.add(MakeEvent(128, 1, r,100, i+3));
            }
            
            sequencer.setSequence(seq);
            sequencer.setTempoInBPM(220);
            sequencer.start();
        }
            
            catch(Exception ex){}
    }
    
    public void controlChange(ShortMessage event){
        System.out.println("la ");
    }
    
    
}

import javax.swing.*;
import javax.sound.midi.*;
import java.awt.*;

public class Panel extends JPanel implements ControllerEventListener{
    boolean msg = false;
    
    public void controlChange(ShortMessage a){
        msg = true;
        repaint();
    }
    
    public void paintComponent(Graphics g){
        if(msg){
            int red = (int)(Math.random() * 127);
            int gre = (int)(Math.random() * 127);
            int blue = (int)(Math.random() * 127);
            
            Color color = new Color(red,gre,blue);
            g.setColor(color);
            
            int x = (int)(Math.random() * 40) + 10;
            int y = (int)(Math.random() * 40) + 10;
            int ht = (int)(Math.random() * 120) + 10;
            int wid = (int)(Math.random() * 120) + 10;
            
            g.fillRect(x, y, wid, ht);
            msg = false;
        }
    }
}

public class Test {
    
    public static void main(String[] args) {
        miniplayer1 play = new miniplayer1();
        play.go();
    }

}

Sequencer（相当于CD播放器）是按照tick（拍）依次检查，1到2到3...

建立一个Sequence的对象seq，给seq的track依次加入MidiEvent

在miniplayer1类中for循环解释为：

向track中加入某个音调的noteOn事件和noteOff事件

中间行向track中加入127类型事件，并且设置在noteOn的同一拍执行

sequencer.addControllerEventListener(panel,eventIwant)表示：

panel想要127事件，当事件源sequencer向panel传递信息，让其repaint

msg的存在是为了让第一次frame被setVisible时不作图