@Override public BytesImpl write(byte[] buffer,int offset,int length){
  while (length > 0) {
    int sublen=Math.min(_data.length - _head,length);
    System.arraycopy(buffer,offset,_data,_head,sublen);
    if (sublen <= 0) {
      throw new UnsupportedOperationException();
    }
    length-=sublen;
    offset+=sublen;
    _head+=sublen;
  }
  return this;
}

@ Override public BytesImpl write ( byte [ ] buffer , int offset , int length ) { while ( length > 0 ) { int sublen = Math . min ( _data . length - _head , length ) ; System . arraycopy ( buffer , offset , _data , _head , sublen ) ; if ( sublen <= 0 ) { throw new UnsupportedOperationException ( ) ; } length -= sublen ; offset += sublen ; _head += sublen ; } return this ; }
adds bytes from the buffer
