java Calendar 类的使用

1. Date → Calendar

public Calendar date2Calendar(Date date){
    Calendar calendar = Calendar.getInstance();
    calendar.setTime(date);
    return calendar;
}
或者
	public static void main(String args[]){
		Date date=new Date();
		Calendar cal=Calendar.getInstance();
		cal.setTime(date);
		System.out.println(cal.get(Calendar.YEAR));
	}

2. Calendar → Date

public Date calendar2Date(Calendar calendar){
    return calendar.getTime();
}
或者

(1) Calendar转化为Date()
Calendar cal=Calendar.getInstance();
Date() date=cal.getTime();
 
(2) Date转化为Calendar
Date date=new Date();
Calendar cal=Calendar.getInstance();
cal.setTime(date);

4. 减一个月

 Calendar calETime = Calendar.getInstance();
  calETime.setTime(customer.getRefundStime());
  calETime.add(Calendar.MONTH,-1);
  // 因为这里的calETime  值事时间类型我要的是字符串所以需要转换一下
  String belongSTime = yearFormat.format(calETime.getTime());
   invoiceRemind.setExpensesBelong(belongSTime+"-"+belongETime);

5. 减三个月

                Calendar calETime = Calendar.getInstance();
                calETime.setTime(customer.getRefundStime());
                calETime.add(Calendar.MONTH,-3);