code: public void wrap(
          final FileChannel fileChannel, final FileChannel.MapMode mapMode, final long offset, final long length)
      {
          unmap();
          this.fileChannel = fileChannel;
          this.mapMode = mapMode;
          map(offset, length);
      }
docs: Remap the buffer based on a new file, mapping mode, offset, and a length
  
  @param fileChannel the file to map
  @param mapMode     for the file when mapping.
  @param offset      the offset of the file to start the mapping
  @param length      of the buffer from the given address