code: public String getExtension(final File file) {
  		if (file != null) {
  			final String fileName = file.getName();
  			final int i = fileName.lastIndexOf('.');
  			if (i > 0 && i < fileName.length() - 1) {
  				return fileName.substring(i + 1).toLowerCase(Locale.getDefault());
  			}
  		}
  		return null;
  	}
docs: Return the extension portion of the file's name.
  
  @return String
  @param file
  File