public void set(Byte o) {
   if (hasPrevious()) {
     m_array.set(m_index, o);
   }
 }
 public Byte previous() {
   if (!hasPrevious()) throw new NoSuchElementException();
   return m_array.get(m_index--);
 }
 public boolean hasNext() {
   return nextIndex() < m_array.size();
 }
 public Byte next() {
   if (!hasNext()) throw new NoSuchElementException();
   return m_array.get(++m_index);
 }
 public void undo() {
   m_bytes.m_bytes = m_old;
 }