code: public SelectionKey register (SelectableChannel chan, int ops, NetEventHandler netEventHandler)
          throws IOException
      {
          SelectionKey key = chan.register(_selector, ops);
          _handlers.put(key, netEventHandler);
          return key;
      }
docs: Registers <code>ops</code> on <code>chan</code> on this manager's selector and hooks
  <code>netEventHandler</code> up to receive events whenever the selection occurs.