FPTextPadding.java

import java.util.Arrays;
import java.util.List;

import static java.lang.String.join;
import static java.util.Collections.emptyList;
import static java.util.Collections.nCopies;
import static java.util.stream.Collectors.toList;


/**
 * Re: https://morgenthum.dev/articles/why-prefer-fp
 *
 * Functional programming approach in Java:
 *  - No variables have their value change.
 *  - Data is not mutated.
 *  - Functions as first-class values, being passed in to other functions.
 */
public class FPTextPadding {

  public static List<String> alignCenter(List<String> text) {
    return text.stream().map(String::length).max(Integer::compareTo).map(maxLen ->
        text.stream().map(s -> {
          int spaceCount = (maxLen - s.length()) / 2;
          return repeat(" ", spaceCount) + s;
        }).collect(toList())).orElse(emptyList());
  }

  static String repeat(String s, int times) {
    // Also provided by Apache Commons, Guava, or Java 11
    return join("", nCopies(times, s));
  }

  public static void main(String[] args) {
    alignCenter(Arrays.asList(args)).forEach(System.out::println);
  }

}

Not a fan of using map twice on line 21, one being Stream.map and the other being Optional.map. There's no reason to not break that onto two lines (other than being in competition with haskell).

Not a fan of using map twice on line 21, one being Stream.map and the other being Optional.map. There's no reason to not break that onto two lines (other than being in competition with haskell).

True. I was pretty much just transliterating their Haskell code to show that Java supports a similar style. Normally I'd assign it to an Optional<Integer> for clarity.