step-by-step.md

Day 5: No "for" loop authorized.

Instead of for loops we can use functions on List

• Let's leverage the power of our IDE

• Our code now looks like this

private StringBuilder formatPopulation() {
    final var response = new StringBuilder();

    population.forEach(person -> {
        response.append(format("%s %s", person.firstName(), person.lastName()));
        if (!person.pets().isEmpty()) {
            response.append(" who owns : ");
        }
        for (var pet : person.pets()) {
            response.append(pet.name()).append(" ");
        }
        if (!population.getLast().equals(person)) {
            response.append(lineSeparator());
        }
    });
    return response;
}

Ok we do not have a for loop anymore, may we go further?

• Let's do it 🚀
  • One way to do it is to not use a StringBuilder anymore but aggregating the String
  • We prepare our refactoring by extracting variables

• Then, we extract method

• Then we move pet logic inside the new method
  • We make the logic independent of the StringBuilder (Pure Function)

private StringBuilder formatPopulation() {
    final var response = new StringBuilder();

    population.forEach(person -> {
        final var formattedPerson = formatPerson(person);
        response.append(formattedPerson);

        if (!population.getLast().equals(person)) {
            response.append(lineSeparator());
        }
    });
    return response;
}

private static String formatPerson(Person person) {
    StringBuilder formattedPerson = new StringBuilder(format("%s %s", person.firstName(), person.lastName()));

    if (!person.pets().isEmpty()) {
        formattedPerson.append(" who owns : ");
        for (var pet : person.pets()) {
            formattedPerson.append(pet.name()).append(" ");
        }
    }
    return formattedPerson.toString();
}

• We can now replace the forEach by the map method (Person -> String)
  • Regarding the lineSeparator() logic we can use a collector

private String formatPopulation() {
    return population.stream()
            .map(PopulationTests::formatPerson)
            .collect(Collectors.joining(lineSeparator()));
}

• We can simplify the formatPerson method as well

private static String formatPerson(Person person) {
    return format("%s %s", person.firstName(), person.lastName()) +
            (!person.pets().isEmpty() ? formatPets(person) : "");
}

private static String formatPets(Person person) {
    return person.pets()
            .stream()
            .map(Pet::name)
            .collect(Collectors.joining(" ", " who owns : ", " "));
}

• Our final version of the code looks like this :

private String formatPopulation() {
    return population.stream()
            .map(PopulationTests::formatPerson)
            .collect(Collectors.joining(lineSeparator()));
}

private static String formatPerson(Person person) {
    return format("%s %s", person.firstName(), person.lastName()) +
            (!person.pets().isEmpty() ? formatPets(person) : "");
}

private static String formatPets(Person person) {
    return person.pets()
            .stream()
            .map(Pet::name)
            .collect(Collectors.joining(" ", " who owns : ", " "));
}

Vavr alternative

By using, alternative collections the code could be a little bit less verbose...

Take a look at it :

private static String formatPopulation() {
    return population
            .map(PopulationWithVavrTests::formatPerson)
            .mkString(lineSeparator());
}

private static String formatPerson(Person person) {
    return format("%s %s", person.firstName(), person.lastName()) +
            (!person.pets().isEmpty() ? formatPets(person) : "");
}

private static String formatPets(Person person) {
    return List.ofAll(person.pets())
            .map(Pet::name)
            .mkString(" who owns : ", " ", " ");
}