code: public static Comparator<File> fileLastModifiedComparator() {
      return (fileOne, fileTwo) -> Long.valueOf(fileOne.lastModified()).compareTo(fileTwo.lastModified());
    }
docs: Returns a {@link Comparator} used to compare two different {@link File}s for order based on their last modified
  timestamp.
  
  @return a {@link Comparator} used to compare {@link File}s for order by their last modified timestamp.
  @see java.io.File#lastModified()
  @see java.lang.Comparable#compareTo(Object)
  @see java.util.Comparator