비슷한 매개변수 목록을 여러 함수에서 사용하고있다면 해당 메서드를 모아서 클래스를 만들수있다.

클래스 내부로 메소드를 얾기고, 데이터를 필드로 만들면 메서드에 전달해야하는 매개변수 목록도 줄일수 있다.

변경전

public class StudyDashboard {

    private final int totalNumberOfEvents;

    public StudyDashboard(int totalNumberOfEvents) {
        this.totalNumberOfEvents = totalNumberOfEvents;
    }

    public static void main(String[] args) throws IOException, InterruptedException {
        StudyDashboard studyDashboard = new StudyDashboard(15);
        studyDashboard.print();
    }

    private void print() throws IOException, InterruptedException {
        GitHub gitHub = GitHub.connect();
        GHRepository repository = gitHub.getRepository("whiteship/live-study");
        List<Participant> participants = new CopyOnWriteArrayList<>();

        ExecutorService service = Executors.newFixedThreadPool(8);
        CountDownLatch latch = new CountDownLatch(totalNumberOfEvents);

        for (int index = 1 ; index <= totalNumberOfEvents ; index++) {
            int eventId = index;
            service.execute(() -> {
                try {
                    GHIssue issue = repository.getIssue(eventId);
                    List<GHIssueComment> comments = issue.getComments();

                    for (GHIssueComment comment : comments) {
                        String username = comment.getUserName();
                        boolean isNewUser = participants.stream().noneMatch(p -> p.username().equals(username));
                        Participant participant = null;
                        if (isNewUser) {
                            participant = new Participant(username);
                            participants.add(participant);
                        } else {
                            participant = participants.stream().filter(p -> p.username().equals(username)).findFirst().orElseThrow();
                        }

                        participant.setHomeworkDone(eventId);
                    }

                    latch.countDown();
                } catch (IOException e) {
                    throw new IllegalArgumentException(e);
                }
            });
        }

        latch.await();
        service.shutdown();

        try (FileWriter fileWriter = new FileWriter("participants.md");
             PrintWriter writer = new PrintWriter(fileWriter)) {
            participants.sort(Comparator.comparing(Participant::username));

            writer.print(header(participants.size()));

            participants.forEach(p -> {
                String markdownForHomework = getMarkdownForParticipant(p.username(), p.homework());
                writer.print(markdownForHomework);
            });
        }
    }

    private String getMarkdownForParticipant(String username, Map<Integer, Boolean> homework) {
        return String.format("| %s %s | %.2f%% |\\n", username, checkMark(homework), getRate(homework));
    }

    /**
     * |:white_check_mark:|:white_check_mark:|:white_check_mark:|:x:|
     */
    private String checkMark(Map<Integer, Boolean> homework) {
        StringBuilder line = new StringBuilder();
        for (int i = 1 ; i <= this.totalNumberOfEvents ; i++) {
            if(homework.containsKey(i) && homework.get(i)) {
                line.append("|:white_check_mark:");
            } else {
                line.append("|:x:");
            }
        }
        return line.toString();
    }

    private double getRate(Map<Integer, Boolean> homework) {
        long count = homework.values().stream()
                .filter(v -> v == true)
                .count();
        return (double) (count * 100 / this.totalNumberOfEvents);
    }

    /**
     * | 참여자 (420) | 1주차 | 2주차 | 3주차 | 참석율 |
     * | --- | --- | --- | --- | --- |
     */
    private String header(int totalNumberOfParticipants) {
        StringBuilder header = new StringBuilder(String.format("| 참여자 (%d) |", totalNumberOfParticipants));

        for (int index = 1; index <= this.totalNumberOfEvents; index++) {
            header.append(String.format(" %d주차 |", index));
        }
        header.append(" 참석율 |\\n");

        header.append("| --- ".repeat(Math.max(0, this.totalNumberOfEvents + 2)));
        header.append("|\\n");

        return header.toString();
    }

}