java得到当月天数

1.使用calendar类实现

/** * 取得当月天数 * */ public static int getCurrentMonthLastDay() { Calendar a = Calendar.getInstance(); a.set(Calendar.DATE, 1);//把日期设置为当月第一天 a.roll(Calendar.DATE, -1);//日期回滚一天，也就是最后一天 int maxDate = a.get(Calendar.DATE); return maxDate; } /** * 得到指定月的天数 * */ public static int getMonthLastDay(int year, int month) { Calendar a = Calendar.getInstance(); a.set(Calendar.YEAR, year); a.set(Calendar.MONTH, month - 1); a.set(Calendar.DATE, 1);//把日期设置为当月第一天 a.roll(Calendar.DATE, -1);//日期回滚一天，也就是最后一天 int maxDate = a.get(Calendar.DATE); return maxDate; }

 

2.使用自己编写的函数实现

 

package test; import java.text.SimpleDateFormat; import java.util.Calendar; import java.util.Date; /** * 日期工具类 by hpf * */ public class DateUtils { //返回当前年月日 String getNowDate() { Date date = new Date(); String nowDate = new SimpleDateFormat("yyyy年MM月dd日").format(date); return nowDate; } //返回当前年份 int getYear() { Date date = new Date(); String year = new SimpleDateFormat("yyyy").format(date); return Integer.parseInt(year); } //返回当前月份 int getMonth() { Date date = new Date(); String month = new SimpleDateFormat("MM").format(date); return Integer.parseInt(month); } //判断闰年 boolean isLeap(int year) { if (((year % 100 == 0) && year % 400 == 0) || ((year % 100 != 0) && year % 4 == 0)) return true; else return false; } //返回当月天数 int getDays(int year, int month) { int days; int FebDay = 28; if (isLeap(year)) FebDay = 29; switch (month) { case 1: case 3: case 5: case 7: case 8: case 10: case 12: days = 31; break; case 4: case 6: case 9: case 11: days = 30; break; case 2: days = FebDay; break; default: days = 0; break; } return days; } //返回当月星期天数 int getSundays(int year, int month) { int sundays = 0; SimpleDateFormat sdf = new SimpleDateFormat("EEEE"); Calendar setDate = Calendar.getInstance(); //从第一天开始 int day; for (day = 1; day <= getDays(year, month); day++) { setDate.set(Calendar.DATE, day); String str = sdf.format(setDate.getTime()); if (str.equals("星期日")) { sundays++; } } return sundays; } public static void main(String[] args) { DateUtils du = new DateUtils(); System.out.println("今天日期是：" + du.getNowDate()); System.out.println("本月有" + du.getDays(du.getYear(), du.getMonth()) + "天"); System.out.println("本月有" + du.getSundays(du.getYear(), du.getMonth()) + "个星期天"); } }