我正在开发一个音乐应用程序，它可以创建一个正方形，并在每次活动中重新绘制屏幕。事件就是声音，我用sound.midi api创建了它们。但是，当我运行应用程序的方块不出现在窗口上！有人能告诉我我做错了什么吗？
这是我的主要课程：

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

public class BeatBoxProject {

static JFrame f = new JFrame ("My first mucic video");
static DrawPanel m1;

public static void main(String[] args) {
BeatBoxProject mini = new BeatBoxProject();
mini.go();
}

public void setUpGui(){
m1 = new DrawPanel();
f.setContentPane(m1);
f.setBounds(30, 30, 300, 300);
f.setVisible(true);
}

public void go(){
setUpGui();

try{  Sequencer player = MidiSystem.getSequencer();  
player.open(); // we need the open the sequencer 

player.addControllerEventListener(m1, new int [] {127});

Sequence seq = new Sequence( Sequence.PPQ, 4); 
Track track = seq.createTrack();  

int r = 0;                        
for (int i = 0; i < 60; i+=4) {

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+2));

}
player.setSequence(seq); // lets put the disk into the player
player.setTempoInBPM(120); // lets set the beat(beat per minutes)
player.start();

}catch (Exception ex){

        ex.printStackTrace();
}
}

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

MidiEvent event  = null;

try{
ShortMessage a = new ShortMessage();
a.setMessage(comd, chan, two, two);
event = new MidiEvent(a,tick);
}catch(Exception e) {}
return event;
}
}

下面是drawpanel类：

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

public class DrawPanel extends JPanel implements ControllerEventListener { 

boolean msg = false; // its false unles we gonna have an event 

public void controlChange(ShortMessage event) {
    msg = true;
    repaint();
}   

public void paintComponent (Graphics g){
if (msg){  // wee need the msg because other thing can repaint the panel but we only want when event occurs 

Graphics2D g2 = (Graphics2D) g;    

int r = (int) (Math.random()* 250); 
int gr = (int) (Math.random()* 250); 
int b = (int) (Math.random()* 250); 

g.setColor(new Color(r,gr,b));

int ht = (int) ((Math.random()*120) +10);
int width = (int) ((Math.random()*120) +10);

int x = (int) ((Math.random()*40) +10);
int y = (int) ((Math.random()*40) +10);

g.fillRect(x, y, width, HEIGHT);
msg=false;

}
}
}