得到某月的天数

Calendar time=Calendar.getInstance();
      time.clear();
      time.set(Calendar.YEAR,2018);
//year年
      time.set(Calendar.MONTH,1);
//Calendar对象默认一月为0,month月
      int day=time.getActualMaximum(Calendar.DAY_OF_MONTH);//本月份的天数
      System.out.println(day);