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);
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);