Calendar 和 Date 之间的相互转换

①Calendar->Date

Calendar cal = Calendar.getInstance();
Date date = cal.getTime();

②Date->Calendar

Date date = new Date();
Calendar cal = Calendar.getInstance();
cal.setTime(date);

创建指定年月日的 Date 对象

通过 Calender 创建

Date createSpecifyDate(int year,int month,int date[,int hour,int minute,int seconds]){
    Calendar cal = Calendar.getInstance();
    Calendar.set(year,month,date[,hour,minute,seconds]);
    Date date = cal.getTime();
    return date;
}

通过 SimpleDateFormat 创建

Date createSpecifyDate(String dateStr) {
        SimpleDateFormat sf = new SimpleDateFormat("yyyy-MM-dd");
        Date date = sf.parse(dateStr);
        return date;
    }

获取指定月份的最大天数

int getMaxDayOfMonth(int year,int month){
     Calendar cal = new GregorianCalendar(year,month,1);
     return  cal.getActualMaximum(Calendar.DAY_OF_MONTH);
}

获取当前年每个时间计量单位常量的总值