Java實現按年月打印日歷功能【基于Calendar】

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
public class CalendarBook {
  public static void main(String[] args) throws ParseException {
    CalendarBook cb = new CalendarBook();
    cb.printWeekTitle();
    cb.printCalendar(2018, 3);
  }
  public void printCalendar(int year, int month) throws ParseException {
    String monthStr; // 格式化月份，因為要轉成yyyyMMdd格式的
    if (month < 10) {
      monthStr = "0" + month;
    } else {
      monthStr = month + ""; // 數字跟字符串拼接轉成字符串格式
    }
    String yearMonthStr = year + monthStr;
    SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd");
    Calendar calendarEnd = Calendar.getInstance();
    Calendar calendarStart = Calendar.getInstance();
    // 根據年份和月份得到輸入月份有多少天
    int monthDays = getMonthLastDay(year, month);
    // 月初的date字符串
    String dateStartStr = yearMonthStr + "01";
    // 月末的date字符串
    String dateEndStr = yearMonthStr + monthDays;
    Date startDate = sdf.parse(dateStartStr);
    Date endDate = sdf.parse(dateEndStr);
    calendarStart.setTime(startDate);
    calendarEnd.setTime(endDate);
    // 得到輸入月份有多少周
    int weeks = calendarEnd.get(Calendar.WEEK_OF_MONTH);
    // 得到當月第一天是星期幾，這里周日為第一天，從1開始，周一則為2
    int dayOfWeek = calendarStart.get(Calendar.DAY_OF_WEEK);
    int day = 1;
    // 當月的第一周做特殊處理，單獨打印一行
    for (int i = 1; i <= 7; i++) {
      if (i >= dayOfWeek) {
        System.out.print(" " + day + " ");
        day++;
      } else {
        System.out.print("  ");
      }
    }
    System.out.println();
    // 開始打印從第二周開始的日期
    for (int week = 1; week < weeks; week++) {
      for (int i = 1; i <= 7; i++) {
        if (day > monthDays) {
          break;
        }
        if (day < 10) {
          System.out.print(" " + day + " ");
        } else {
          System.out.print(day + " ");
        }
        day++;
      }
      System.out.println();
    }
  }
  public int getMonthLastDay(int year, int month) {
    int monthDay;
    int[][] day = { { 0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 },
        { 0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 } };
    if (year % 4 == 0 && year % 100 != 0 || year % 400 == 0) {
      // 閏年
      monthDay = day[1][month];
    } else {
      monthDay = day[0][month];
    }
    return monthDay;
  }
  public void printWeekTitle() {
    System.out.println("日" + "   " + "一" + "   " + "二" + "   " + "三"
        + "   " + "四" + "   " + "五" + "   " + "六");
  }
}