自学java，自定义字节流缓冲区时，小弟有一处代码无法理解，请各位指点迷津,该如何处理

/*需求自定义字节流缓冲区*/import java.io.*;class MyBufferedInputStream{    private InputStream in;    private byte[] buf = new byte[1024*4];    private int pos = 0,count = 0;        MyBufferedInputStream(InputStream in)    {        this.in = in;    }        //一次读一个字符，从缓冲区(字节数组)获取    public int myRead()throws IOException    {        //返回为int类型是为了提升返回值的类型        //通过in对象读取硬盘上数据，并储存buf中        if (count==0)        {            count = in.read(buf);            if(count<0)                return -1;            pos = 0;            byte b = buf[pos];            count--;            pos++;                        return b&255;        }        else        {            byte b = buf[pos];            count--;            pos++;                        return b&0xff;                    }            }    public void myClose()throws IOException    {        in.close();    }            }class MyBufferedInputStreamDemo{    public static void main(String[] args)throws IOException    {        myCopyMusic();    }    public static void myCopyMusic()throws IOException    {        MyBufferedInputStream mbis = new MyBufferedInputStream(new FileInputStream("F:\\2.mp3"));        BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream("F:\\1.mp3"));        int ch = 0;                while((ch=mbis.myRead())!=-1)        {            bos.write(ch);        }        bos.close();        mbis.myClose();    }}