How to remove this issue about NumberFormatException?

Hi, all:

    I am rookie for coding java and I have one question about queue
class

    I use one queue class: ArrayBlockingQueue to save/get my data

    I read some data from HW and save into one ArrayBlockingQueue, and
then get from this ArrayBlockingQueue when needing. But it has one
error message: <java.lang.NumberFormatException: Invalid int:
"ffffff94"> when doing poll function

    My simple code is below

    private ArrayBlockingQueue<Byte> iReadQueueArray = new
ArrayBlockingQueue<Byte>(READBUF_SIZE, true);

    byte[] rbuf = new byte[256];

    iReadCnt = readfromHW(rbuf, rbuf.length); <---read data from
HW
    ret = iReadQueueArray.offer( Byte.valueOf( (rbuf[i]&0xFF) ));

//-----------------------------------------------------------------------//
    public int read(byte[] buf) {
      Byte mdata;
      ...
      mdata = (Byte)iReadQueueArray.poll(); <---occur error when
polling some data
      if( mdata!=null ) {
          buf[i] = (byte) (mdata.byteValue()&0xFF);
      }
      ...
      return 0;
    }
//-----------------------------------------------------------------------//

    How to modify offer data into the queue and poll data from the
queue?

    Thank you for your help!

BR,
Alan