public class FunctorExample {
  private static Optional<integer> readInt(final Scanner reader) {
    if (reader.hasNextInt()) {
      return Optional.of(reader.nextInt());
    } else {
      return Optional.empty();
    }
  }

  private static long compute(int i) {
    return i * i;
  }

  private static void display(final Optional<Long> result) {
    if (result.isPresent()) {
      System.out.println(result.get());
    } else {
      System.out.println("You don't give me an integer :-(");
    }
  }

  public static void main(String args[]) {
    System.out.println("Give me an integer");
    final Optional<Integer> optionalInt = readInt(new Scanner(System.in));
    Optional<Long> result = optionalInt.map(FunctorExample::compute);
    display(result);
  }
}