获取两个日期之间的相差月份

public static double getIntervalMonths(String openDate, String applyTime) {
DateFormat df = new SimpleDateFormat("yyyy-MM-dd");
Calendar firstDate = Calendar.getInstance();// 申请时间（后时间）
Calendar secDate = Calendar.getInstance();// 前时间
double months = 0;// 相隔多少月
try {
if (applyTime != null || !"".equals(applyTime)) {
firstDate.setTime(df.parse(applyTime));
}
Date opDate = df.parse(openDate);
secDate.setTime(opDate);
long firstDateMill = firstDate.getTimeInMillis();
long secDateMill = secDate.getTimeInMillis();
long days = (firstDateMill - secDateMill) / (1000 * 60 * 60 * 24);// 相隔天数
months = days / 30.0;
} catch (ParseException e) {
e.printStackTrace();
}

return months;
}