byte[] dataBuf = new byte[512];
DatagramPacket packet;
    
try
{
   int length = 0;
   ……
   dataBuf[1]=0xB5;
             ^^^^^^
   ……
   packet = new DatagramPacket(dataBuf,length,InetAddress.getByName(……), ……);
}catch(Exception e)
{
    System.out.println(e.toString());
}