结论：

Question

当我执行下面的代码时，我得到相同的输出。

public static void main(String[] args) throws ParseException {    
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
    Date procDate = sdf.parse("2016-01-01");
    Calendar cal = Calendar.getInstance(Locale.UK);
    cal.setFirstDayOfWeek(Calendar.SUNDAY);
    cal.setTime(procDate);
    System.out.println(cal.get(Calendar.WEEK_OF_YEAR) ); 
    System.out.println(cal.get(Calendar.YEAR) );

    procDate = sdf.parse("2016-12-27");
    cal.setTime(procDate);
    System.out.println(cal.get(Calendar.WEEK_OF_YEAR) ); 
    System.out.println(cal.get(Calendar.YEAR) );            
}

实际输出：

52
  2016
  52个
  2016

预期产出：

52
  2015年
  52个
  2016

或者

0
  2016
  52个
  2016

Locale和setFirstDayOfWeek是我无法改变的。

Answer 1

让我引用消息来源：

/**
 * Field number for <code>get</code> and <code>set</code> indicating the
 * week number within the current year.  The first week of the year, as
 * defined by <code>getFirstDayOfWeek()</code> and
 * <code>getMinimalDaysInFirstWeek()</code>, has value 1.  Subclasses define
 * the value of <code>WEEK_OF_YEAR</code> for days before the first week of
 * the year.
 *
 * @see #getFirstDayOfWeek
 * @see #getMinimalDaysInFirstWeek
 */

让我们看看这个实验：

public static void main(String[] args) throws ParseException {
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
    Date procDate = sdf.parse("2016-01-01");
    Calendar cal = Calendar.getInstance(Locale.UK);
    cal.setFirstDayOfWeek(Calendar.SUNDAY);
    cal.setTime(procDate);
    System.out.println(cal.get(Calendar.WEEK_OF_YEAR) );
    System.out.println(cal.get(Calendar.YEAR) );
    cal.add(Calendar.DAY_OF_YEAR, 1);
    System.out.println(cal.get(Calendar.WEEK_OF_YEAR) );
    System.out.println(cal.get(Calendar.YEAR) );
    cal.add(Calendar.DAY_OF_YEAR, 1);
    System.out.println(cal.get(Calendar.DAY_OF_YEAR));
    System.out.println(cal.get(Calendar.WEEK_OF_YEAR) );
    System.out.println(cal.get(Calendar.YEAR) );

    procDate = sdf.parse("2016-12-27");
    cal.setTime(procDate);
    System.out.println(cal.get(Calendar.WEEK_OF_YEAR) );
    System.out.println(cal.get(Calendar.YEAR) );
}

52
  2016
  52个
  2016
  3
  1
  2016
  52个
  2016

结论：

WEEK_OF_YEAR在一年中的整周的第一天设置为1。在此之前，它取决于实施。在默认的Java实现中，默认情况下为52。您可以设置cal.setMinimalDaysInFirstWeek(1);然后它应该修复您的情况。

为什么呢？询问Sun的人。

Answer 2

Calendar类不知道您的

调用

cal.get(Calendar.WEEK_OF_YEAR); 
cal.get(Calendar.YEAR);

应该是一起关系。因为在X年的最后一周，你可能意味着你已经在X + 1年级，你所看到的输出实际上是正确的。

要想要你想要的东西你应该使用另一个DateFormater打印出一年中的一周以及相应的年份：

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
SimpleDateFormat sdf2 = new SimpleDateFormat("w Y");
Date procDate = sdf.parse("2016-01-01");
System.out.println(sdf2.format(procDate));

procDate = sdf.parse("2016-12-27");
System.out.println(sdf2.format(procDate));

结果：

53 2015
52 2016

Answer 3

看到这个答案

Understanding java.util.Calendar WEEK_OF_YEAR

这个问题与java一年中不合理使用这个星期有关。无论如何，调用cal.setMinimalDaysInFirstWeek(3);将修复结果（就差异而言。在我的情况下，1月stil给了我第53周（！）

Answer 4

回到本周的开始日我得到了预期的结果。在我的情况下，星期日是一周的开始日。所以我设置了cal.set(Calendar.DAY_OF_WEEK, Calendar.SUNDAY)，这解决了我的问题。

public static void main(String[] args) throws ParseException {
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
    Date procDate = sdf.parse("2016-01-01");
    Calendar cal = Calendar.getInstance(Locale.UK);
    cal.setFirstDayOfWeek(Calendar.SUNDAY);
    cal.setTime(procDate);
    cal.set(Calendar.DAY_OF_WEEK, Calendar.SUNDAY); //Starting day of week
    System.out.println(cal.get(Calendar.WEEK_OF_YEAR) ); 
    System.out.println(cal.get(Calendar.YEAR) );

    procDate = sdf.parse("2016-12-27");
    cal.setTime(procDate);
    cal.set(Calendar.DAY_OF_WEEK, Calendar.SUNDAY); //Starting day of week
    System.out.println(cal.get(Calendar.WEEK_OF_YEAR) ); 
    System.out.println(cal.get(Calendar.YEAR) );            
}

输出：

52
  2015年
  52个
  2016

两个日期

4 个答案:

结论：