如何在Java中找到前兩個星期一的日期？

Question

可能是這樣的：

for(int i=0;i<15;i++){ 
Calendar cal = new GregorianCalendar(); 
cal.add(Calendar.DAY_OF_MONTH, -1); 

if (cal.Calendar.DAY_OF_WEEK==1){ 
System.out.println(cal.cal.getTime()) 

但是可能存在更簡單的方法？ 謝謝。

Answer 1

您正處在正確的軌道上。

Calendar cal = Calendar.getInstance(); 
cal.add(Calendar.DAY_OF_YEAR, -7); // First week before 
cal.add(Calendar.DAY_OF_YEAR, -7); // Second week before 

讓我做這個工作只是星期一。

Calendar cal = Calendar.getInstance(); 

int weekday = cal.get(Calendar.DAY_OF_WEEK); 
int days = (Calendar.SATURDAY - weekday + 2) % 7; 

cal.add(Calendar.DAY_OF_YEAR, days); 

cal.add(Calendar.DAY_OF_MONTH, -7); 
cal.add(Calendar.DAY_OF_MONTH, -7); 

Answer 2

即使簡單的是直接設置平日：

Calendar cal = Calendar.getInstance(); 
cal.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY); 
cal.add(Calendar.DATE, -7); 
System.out.println(cal.getTime()); 

請記住，這不會影響時間。如果你想要00:00，您需要設置相應的值：

cal.set(Calendar.HOUR_OF_DAY, 0); 
cal.set(Calendar.MINUTE, 0); 
cal.set(Calendar.SECOND, 0); 
cal.set(Calendar.MILLISECOND, 0); 

Answer 3

java.time

使用TemporalAdjuster。

LocalDate today = LocalDate.now(); 

LocalDate previousOrSameMonday = today.with(TemporalAdjusters.previousOrSame(DayOfWeek.MONDAY)); 

並減去一週得到第二個。

LocalDate secondMondayBefore = previousOrSameMonday.minusWeeks(1);