Question

我有什么：今天的日期对象。

我需要的是：将包含周的日期存储在ArrayList中。

我尝试了什么：

public static void main(String[] args) {

    Date today = new Date();

    Calendar cal = Calendar.getInstance();
    cal.setFirstDayOfWeek(Calendar.MONDAY);
    cal.setTime(today);

    List<Calendar> daysOfWeek = new ArrayList<>();

    IntStream
            .iterate(2, n -> n+1)
            .limit(7)
            .forEach(n ->
                {  
                    if(n != 8){
                        cal.set(Calendar.DAY_OF_WEEK, n);
                    }else{
                        cal.set(Calendar.DAY_OF_WEEK, 1);
                    }
                    System.out.println("CAL_INSIDE:  " + cal.getTime());
                    daysOfWeek.add(cal);
                });
             System.out.println("");
            daysOfWeek.stream().forEach( cal -> System.out.println("CAL_OUTSIDE: " + cal.getTime()));
}

在forEach语句中，我得到的正是我想要的。但是ArrayList似乎只包含最后一个Date。的输出：

CAL_INSIDE:  Mon Aug 03 14:35:37 CEST 2015
CAL_INSIDE:  Tue Aug 04 14:35:37 CEST 2015
CAL_INSIDE:  Wed Aug 05 14:35:37 CEST 2015
CAL_INSIDE:  Thu Aug 06 14:35:37 CEST 2015
CAL_INSIDE:  Fri Aug 07 14:35:37 CEST 2015
CAL_INSIDE:  Sat Aug 08 14:35:37 CEST 2015
CAL_INSIDE:  Sun Aug 09 14:35:37 CEST 2015

CAL_OUTSIDE: Sun Aug 09 14:35:37 CEST 2015
CAL_OUTSIDE: Sun Aug 09 14:35:37 CEST 2015
CAL_OUTSIDE: Sun Aug 09 14:35:37 CEST 2015
CAL_OUTSIDE: Sun Aug 09 14:35:37 CEST 2015
CAL_OUTSIDE: Sun Aug 09 14:35:37 CEST 2015
CAL_OUTSIDE: Sun Aug 09 14:35:37 CEST 2015
CAL_OUTSIDE: Sun Aug 09 14:35:37 CEST 2015

基本上我得到了我想要的但是......

问题：为什么只有星期日存储在ArrayList中？我错过了什么？

修改

根据接受的答案输出：

CAL_INSIDE:  Mon Aug 03 14:51:31 CEST 2015
CAL_INSIDE:  Tue Aug 04 14:51:31 CEST 2015
CAL_INSIDE:  Wed Aug 05 14:51:31 CEST 2015
CAL_INSIDE:  Thu Aug 06 14:51:31 CEST 2015
CAL_INSIDE:  Fri Aug 07 14:51:31 CEST 2015
CAL_INSIDE:  Sat Aug 08 14:51:31 CEST 2015
CAL_INSIDE:  Sun Aug 09 14:51:31 CEST 2015

CAL_OUTSIDE: Mon Aug 03 14:51:31 CEST 2015
CAL_OUTSIDE: Tue Aug 04 14:51:31 CEST 2015
CAL_OUTSIDE: Wed Aug 05 14:51:31 CEST 2015
CAL_OUTSIDE: Thu Aug 06 14:51:31 CEST 2015
CAL_OUTSIDE: Fri Aug 07 14:51:31 CEST 2015
CAL_OUTSIDE: Sat Aug 08 14:51:31 CEST 2015
CAL_OUTSIDE: Sun Aug 09 14:51:31 CEST 2015

Answer 1

Calendar是一个可变对象，因此您只需存储对该对象的引用，而CAL_OUTSIDE仅为您提供引用Calendar对象的最后一个内部状态的7倍。

你必须搬家

Calendar cal = Calendar.getInstance();
cal.setFirstDayOfWeek(Calendar.MONDAY);
cal.setTime(today);

在循环内部获取7个不同的Calendar个对象。

在ArrayList中存储Java日历会导致意外行为

1 个答案: