資金結算求佔有時間  結算 已知結算日，和提前贖回時間，求上期結算日期，和下期結算日期，並求佔了多少天

public static void getCurrentMonthAndNextMonth(int payDay,Date advanceDate) {

Date modelDate;
Date nextPeriodDate;
Calendar cal= Calendar.getInstance();  
int lastDay = cal.getActualMaximum(Calendar.DAY_OF_MONTH);
System.out.println("當前月最大天數:" + lastDay);
if(payDay <= lastDay){
cal.set(Calendar.DAY_OF_MONTH, payDay);
}else{
cal.set(Calendar.DAY_OF_MONTH, lastDay);
}
Date currentPeriodDate = cal.getTime();
System.out.println(new SimpleDateFormat("yyyy-MM-dd").format(cal.getTime()));
if(currentPeriodDate.before(advanceDate)){
cal.set(Calendar.MONTH, cal.get(Calendar.MONTH)+1);
int nextLastDay = cal.getActualMaximum(Calendar.DAY_OF_MONTH);
System.out.println("下個月最大天數:" + nextLastDay);
if(payDay <= nextLastDay){
cal.set(Calendar.DAY_OF_MONTH, payDay);
}else{
cal.set(Calendar.DAY_OF_MONTH, lastDay);
}
nextPeriodDate = cal.getTime();
System.out.println(new SimpleDateFormat("yyyy-MM-dd").format(cal.getTime()));
}else{
cal.set(Calendar.MONTH, cal.get(Calendar.MONTH)-1);
int nextLastDay = cal.getActualMaximum(Calendar.DAY_OF_MONTH);
System.out.println("上個月最大天數:" + nextLastDay);
if(payDay <= nextLastDay){
cal.set(Calendar.DAY_OF_MONTH, payDay);
}else{
cal.set(Calendar.DAY_OF_MONTH, lastDay);
}
modelDate = cal.getTime();
nextPeriodDate = currentPeriodDate;
currentPeriodDate = modelDate;
System.out.println(new SimpleDateFormat("yyyy-MM-dd").format(cal.getTime()));
}
int currentPeriodDays = daysBetween(currentPeriodDate,nextPeriodDate);
System.out.println("當前期有："+ currentPeriodDays +"天");
int holdDays = daysBetween(currentPeriodDate, advanceDate);
System.out.println("使用者持有天數："+ holdDays +"天");
}