code: private void init(FileChannel channel, FileChannel.MapMode mapMode)
      throws IOException {
          
          this.channel = channel;
          this.mappedByteBuffer = channel.map(mapMode, 0L, channel.size());
          mappedByteBuffer.load();
      }
docs: initializes the channel and mapped bytebuffer
  @param channel FileChannel
  @param mapMode FileChannel.MapMode
  @throws IOException