public void write(byte[] b,int off,int len) throws IOException {
  out.write(b,off,len);
  cksum.update(b,off,len);
}

public void write ( byte [ ] b , int off , int len ) throws IOException { out . write ( b , off , len ) ; cksum . update ( b , off , len ) ; }
writes an array of bytes . will block until the bytes are actually written .
