import java.util.Calendar;
import java.util.Date;
public class DateCalculator {
    public static Date calculateDate(Date startDate, Date endDate, int dayOfWeek) {
        Calendar startCal = Calendar.getInstance();
        startCal.setTime(startDate);
        Calendar endCal = Calendar.getInstance();
        endCal.setTime(endDate);
        // 確保輸入的dayOfWeek在正確的范圍內(nèi)（1-7，其中1代表周一，7代表周日）
        if (dayOfWeek < 1 || dayOfWeek > 7) {
            throw new IllegalArgumentException("Invalid dayOfWeek value. Must be between 1 and 7.");
        }
        // 將輸入的dayOfWeek轉(zhuǎn)換為Calendar的周幾（Calendar.MONDAY, Calendar.SUNDAY等）
        int targetDay = dayOfWeek + 1; // 因?yàn)镃alendar的周日是1，周一到周六依次遞增
        // 查找開(kāi)始日期之后的第一個(gè)目標(biāo)周幾的日期
        while (startCal.getTime().before(endDate)) {
            if (startCal.get(Calendar.DAY_OF_WEEK) == targetDay) {
                break;
            }
            startCal.add(Calendar.DAY_OF_MONTH, 1);
        }
        return startCal.getTime();
    }
    public static void main(String[] args) throws Exception {
        long startDateTimestamp = 1377753600000L; // 開(kāi)始日期的Unix時(shí)間戳，例如2013-09-01 00:00:00
        long endDateTimestamp = 1380345600000L; // 結(jié)束日期的Unix時(shí)間戳，例如2013-10-01 00:00:00
        int targetDayOfWeek = 3; // 周三（在Java中，1=Monday, 7=Sunday）
        Date startDate = new Date(startDateTimestamp);
        Date endDate = new Date(endDateTimestamp);
        Date calculatedDate = calculateDate(startDate, endDate, targetDayOfWeek);
        if (calculatedDate != null) {
            System.out.println("The next occurrence of " + targetDayOfWeek + " (Wednesday) between " 
                              + startDate + " and " + endDate + " is on: " + calculatedDate);
        } else {
            System.out.println("There is no occurrence of the specified weekday between the given dates.");
        }
    }
}

import java.time.DayOfWeek;
import java.time.LocalDate;
import java.time.temporal.TemporalAdjusters;
public class DateCalculator {
    public static LocalDate calculateDate(LocalDate startDate, LocalDate endDate, int dayOfWeek) {
        // 確保輸入的dayOfWeek在正確的范圍內(nèi)（1-7，其中1代表周一，7代表周日）
        if (dayOfWeek < 1 || dayOfWeek > 7) {
            throw new IllegalArgumentException("Invalid dayOfWeek value. Must be between 1 and 7.");
        }
        // 將輸入的dayOfWeek轉(zhuǎn)換為DayOfWeek枚舉值
        DayOfWeek targetDay = DayOfWeek.of(dayOfWeek);
        // 查找開(kāi)始日期之后的第一個(gè)目標(biāo)周幾的日期
        LocalDate firstOccurrence = startDate.with(TemporalAdjusters.nextOrSame(targetDay));
        // 如果第一個(gè)出現(xiàn)的日期在結(jié)束日期之后，則返回null，表示在指定區(qū)間內(nèi)沒(méi)有找到符合條件的日期
        if (firstOccurrence.isAfter(endDate)) {
            return null;
        }
        return firstOccurrence;
    }
    public static void main(String[] args) {
        LocalDate startDate = LocalDate.of(2023, 9, 1); // 開(kāi)始日期
        LocalDate endDate = LocalDate.of(2023, 9, 30); // 結(jié)束日期
        int targetDayOfWeek = 3; // 周三（在Java中，1=Monday, 7=Sunday）
        LocalDate calculatedDate = calculateDate(startDate, endDate, targetDayOfWeek);
        if (calculatedDate != null) {
            System.out.println("The next occurrence of " + targetDayOfWeek + " (Wednesday) between " 
                              + startDate + " and " + endDate + " is on: " + calculatedDate);
        } else {
            System.out.println("There is no occurrence of the specified weekday between the given dates.");
        }
    }
}