Subject_05.java

import java.time.LocalDate;
import java.util.Scanner;

public class Main {
    public static String makeCalendar(int year, int month, int maxLines) {
        int date = 1;       // 일
        int day;            // 요일

        LocalDate firstDate = LocalDate.of(year, month, date); // 해당월 1일 설정
        day = firstDate.getDayOfWeek().getValue();

        StringBuilder calendarString = new StringBuilder();
        calendarString.append(month >= 10 ?
                String.format("[%d년 %d월]\t\t\t\t\n", year, month) : String.format("[%d년 %02d월]\t\t\t\t\n", year, month));
        calendarString.append("일\t월\t화\t수\t목\t금\t토\t\n");

        for (int i = 1; i <= 6; i++) {
            for (int j = 0; j < 7; j++) {
                if (i == 1 && j < day) {
                    calendarString.append("\t");
                } else if (date <= firstDate.lengthOfMonth()) {
                    calendarString.append(String.format("%02d\t", date++));
                } else {
                    calendarString.append("\t");
                }
            }
            calendarString.append("\n");
        }

        return calendarString.toString();
    }

    public static void main(String[] args) {
        int year;
        int month;

        Scanner scanner = new Scanner(System.in);

        while (true) {
            System.out.println("[달력 출력 프로그램]");
            System.out.print("달력의 년도를 입력해 주세요. (yyyy) : ");
            year = scanner.nextInt();
            if (year < 0) {
                System.out.println("년도 입력이 잘못되었습니다. 다시 시작합니다.\n");
                continue;
            }

            System.out.print("달력의 월을 입력해 주세요. (mm) : ");
            month = scanner.nextInt();
            if (month <= 0 || month > 12) {
                System.out.println("월 입력이 잘못되었습니다. 다시 시작합니다.\n");
                continue;
            }
            break;
        }

        System.out.println();

        int lastMonth = month - 1;
        int lastYear = year;

        int nextMonth = month +1 ;
        int nextYear = year;

        if (lastMonth == 0) {
            lastMonth = 12;
            lastYear--;
            nextYear = year;
            nextMonth = month +1;
        } else if (nextMonth == 13) {
            nextMonth = 1;
            nextYear ++;
            lastMonth = month -1;
            lastYear = year;
        }


        String calendarLast = makeCalendar(lastYear, lastMonth, 6);
        String calendarCurrent = makeCalendar(year, month, 6);
        String calendarNext = makeCalendar(nextYear, nextMonth, 6);

        String[] linesLast = calendarLast.split("\n");
        String[] linesCurrent = calendarCurrent.split("\n");
        String[] linesNext = calendarNext.split("\n");

        int maxLength = Math.max(Math.max(linesLast.length, linesCurrent.length), linesNext.length);

        for (int i = 0; i < maxLength; i++) {
            String lastLine = i < linesLast.length ? linesLast[i] : "";
            String currentLine = i < linesCurrent.length ? linesCurrent[i] : "";
            String nextLine = i < linesNext.length ? linesNext[i] : "";
            System.out.println(lastLine + "\t" + currentLine + "\t" + nextLine);
        }
    }
}