如何從今天開始獲取最后兩個星期五的日期？

Question

我需要使用今天的日期來獲取最近兩個星期五的日期。這是我當前使用的公共類GetDate {

public static void main(String[] args) {
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
    Date dt = new Date();
    Calendar c = Calendar.getInstance();
    c.setTime(dt);
    System.out.println("today : " + sdf.format(dt));
    while (c.get(Calendar.DAY_OF_WEEK) != 6) {
        c.add(Calendar.DATE, -1);
    }
    Date lastFri=c.getTime();
    System.out.println("last fri : "+sdf.format(lastFri));
    c.add(Calendar.DATE, -7);
    Date prevFri = c.getTime();
    System.out.println("previous friday : "+sdf.format(prevFri));

    }


}

有什么方法可以優化此代碼？

Answer 1

在Java 8，如果你沒有使用日歷API，你可以使用一個TemporalAdjuster ：

LocalDate today = LocalDate.now();
LocalDate prevFriday = today.with(previous(FRIDAY));
LocalDate prevPrevFriday = prevFriday.with(previous(FRIDAY));

_{注意：需要以下靜態導入
import static java.time.temporal.TemporalAdjusters.previous;
import static java.time.DayOfWeek.FRIDAY;}

Answer 2

您可以這樣獲得最后一個星期五：

Calendar cal = Calendar.getInstance();
cal.add(Calendar.WEEK_OF_YEAR, -1);
cal.set(Calendar.DAY_OF_WEEK, Calendar.FRIDAY);

通過減去一個星期並將星期幾設置為星期五，可以得到最后一個星期五。

Answer 3

嘗試類似：

cal.add(Calendar.WEEK_OF_YEAR, -1);
cal.set(Calendar.DAY_OF_WEEK, Calendar.FRIDAY);
Date lastFriday = cal.getTime();
cal.add(Calendar.WEEK_OF_YEAR, -1);
cal.set(Calendar.DAY_OF_WEEK, Calendar.FRIDAY);
Date lastToLastFriday = cal.getTime();

Answer 4

此行應有幫助：

calendar.add(Calendar.DATE, Calendar.FRIDAY - 7 - c.get(Calendar.DAY_OF_WEEK));

因此，這段代碼正在解決您的問題：

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
Calendar c = GregorianCalendar.getInstance();
c.add(Calendar.DATE, Calendar.FRIDAY - 7 - c.get(Calendar.DAY_OF_WEEK));
System.out.println(sdf.formate(c.getTime()));
c.add(Calendar.DATE, Calendar.FRIDAY - 14 - c.get(Calendar.DAY_OF_WEEK));
System.out.println(sdf.formate(c.getTime()));