code: public void registerChannel(FileChannel channel, boolean writable) {
  		readableChannels.add(channel);
  		if (writable) {
  			writableChannels.add(channel);
  		}
  	}
docs: Makes the given channel a candidate to read (always) and write (only if writable) ciphertext from/to.
  
  @param channel
  @param writable