code: public static String getRandomFilename(final String prefix) {
  
  		final StringBuilder stringBuilder = new StringBuilder(prefix);
  
  		for (int i = 0; i < LENGTH; i++) {
  			stringBuilder.append(ALPHABET[(int) Math.floor(Math.random() * (double) ALPHABET.length)]);
  		}
  
  		return stringBuilder.toString();
  	}
docs: Constructs a random filename with the given prefix and
  a random part generated from hex characters.
  
  @param prefix
  the prefix to the filename to be constructed
  @return the generated random filename with the given prefix