static代表“每个类一个”而不是“每个对象一个”。即静态变量是类的所有对象共有的。

1 static JFrame f;

 static MyDrawPanel ml;

 import javax.sound.midi.ControllerEventListener;

 import javax.sound.midi.MidiEvent;

 import javax.sound.midi.MidiSystem;

 import javax.sound.midi.Sequence;

 import javax.sound.midi.Sequencer;

 import javax.sound.midi.ShortMessage;

 import javax.sound.midi.Track;

 import javax.swing.JFrame;

 import javax.swing.*;

 import java.awt.*;

 import java.io.*;

 public class MiniMusicPlayer3 {

        //JFrame frame;

     static JFrame f=new JFrame("My first music Video");

     static MyDrawPanel ml;

    public static void main(String[] args){

        MiniMusicPlayer3 mini=new MiniMusicPlayer3();

        mini.go();

    }

    public void go(){

        //frame=new JFrame("My first music Video");

        //MyDrawPanel myDraw=new MyDrawPanel();

        ml=new MyDrawPanel();

        //f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        f.getContentPane().add(ml);

        //f.getContentPane(ml);

        f.setBounds(,,,);

        f.setVisible(true);

        try{

        Sequencer player=MidiSystem.getSequencer();

        player.open();

        int[] eventsIWant={};

        player.addControllerEventListener(ml,eventsIWant);

        Sequence sequence=new Sequence(Sequence.PPQ,);//什么意思，待会查一查。

        Track track=sequence.createTrack();

        int r=;

        for(int i=;i<;i+=){

            r=(int) ((Math.random()*)+);

            track.add(makeEvent(,,r,,i));

            track.add(makeEvent(,,,,i));

            track.add(makeEvent(,,r,,i+));

        }

        player.setSequence(sequence);

        player.setTempoInBPM();

        player.start();

        }catch(Exception ex){ex.printStackTrace();}

    }

    public MidiEvent makeEvent (int comd,int chan,int one,int two,int tick){

         MidiEvent event=null;

         try{

             ShortMessage a=new ShortMessage();

             a.setMessage(comd,chan,one,two);

             event=new MidiEvent(a,tick);

         }catch(Exception e) {}

         return event;

     }

    class MyDrawPanel extends JPanel implements ControllerEventListener{

        boolean msg=false;

        public void controlChange(ShortMessage event){

            msg=true;

            repaint();

        }

        public void paintComponent(Graphics g){

            if(msg){

                Graphics2D g2d=(Graphics2D) g;

                int red=(int) (Math.random()*);

                int green=(int) (Math.random()*);

                int blue=(int) (Math.random()*);

                Color randomColor=new Color(red,green,blue);

                g2d.setColor(randomColor);

                int ht=(int) ((Math.random()*)+);

                int width=(int) ((Math.random()*)+);

                int x=(int) ((Math.random()*)+);

                int y=(int) ((Math.random()*)+);

                g.fillRect(x, y, width, ht);

                msg=false;

            }

        }

 }

 }