在Java中的日期范围内获取所有星期五 [英] Get all Fridays in a date Range in Java
问题描述
以下是我的代码：
public class Friday {
public static void main（String [] args）{
String start =01/01/2009;
String end =12/09/2013;
String [] startTokens = start.split（/）;
String [] endTokens = end.split（/）;
日历startCal = new GregorianCalendar（Integer.parseInt（startTokens [2]），Integer.parseInt（startTokens [1]） - 1，Integer.parseInt（startTokens [0]））;
日历endCal = new GregorianCalendar（Integer.parseInt（endTokens [2]），Integer.parseInt（endTokens [1]） - 1，Integer.parseInt（endTokens [0]））;
int startYear = Integer.parseInt（startTokens [2]）;
int endYear = Integer.parseInt（endTokens [2]）;
int startWeek = startCal.get（Calendar.WEEK_OF_YEAR）;
int endWeek = endCal.get（Calendar.WEEK_OF_YEAR）;
日历cal = new GregorianCalendar（）;
cal.set（Calendar.DAY_OF_WEEK，Calendar.FRIDAY）;
// cal.setMinimalDaysInFirstWeek（7）;
ArrayList< String> main = new ArrayList< String>（）;
while（startYear< = endYear）{
cal.set（Calendar.YEAR，startYear）;
System.out.println（cal.getMinimalDaysInFirstWeek（））;
if（startYear == endYear）{
main.addAll（getFridays（startWeek，endWeek，cal））;
}
else {
main.addAll（getFridays（startWeek，52，cal））;
startWeek = 1;
}
startYear = startYear +1;
}
for（String s：main）{
System.err.println（s）;
}
}
public static ArrayList< String> getFridays（int startWeek，int endWeek，Calendar cal）{
ArrayList< String> fridays = new ArrayList< String>（）;
while（startWeek< = endWeek）{
cal.set（Calendar.WEEK_OF_YEAR，startWeek）;
fridays.add（cal.getTime（）。toString（））;
startWeek = startWeek +1
}
返回星期五;
}
}
现在，当我运行代码时，我注意到星期五2011年失踪经过一些调试和在线浏览，我认为 Calendar.WEEK_OF_YEAR 是区域设置，我必须使用 setMinimalDaysInFirstWeek（7）修改它。
所以取消注释上面的代码中的相关行。
从我以前了解的第一个每周的一周应从一整个星期开始。
例如2010年1月1日星期五。但是，由于我配置了这个星期从1月3日开始，所以不应该显示在结果中。但现在我仍然看到1月1日星期五
我非常困惑。有些人可以解释为什么会发生这种情况吗？
这些Stackoverflow文章帮助了我一些：
了解java.util.Calendar WEEK_OF_YEAR
这是一个更简单的方法，使用精彩 http://www.joda.org/joda-time/ 图书馆：
String start =01/01/2009;
String end =12/09/2013;
DateTimeFormatter模式= DateTimeFormat.forPattern（dd / MM / yyyy）;
DateTime startDate = pattern.parseDateTime（start）;
DateTime endDate = pattern.parseDateTime（end）;
列表< DateTime> fridays = new ArrayList<>（）;
while（startDate.isBefore（endDate））{
if（startDate.getDayOfWeek（）== DateTimeConstants.FRIDAY）{
fridays.add（startDate）;
}
startDate = startDate.plusDays（1）;
}
在这个结尾，你会有星期五的星期五阵列。简单吗？
或者如果你想加快速度，一旦你有一个星期五，你可以从使用天数切换到使用周：
String start =01/01/2009;
String end =12/09/2013;
DateTimeFormatter pattern = DateTimeFormat.forPattern（dd / MM / yyyy）;
DateTime startDate = pattern.parseDateTime（start）;
DateTime endDate = pattern.parseDateTime（end）;
列表< DateTime> fridays = new ArrayList<>（）;
boolean reachAFriday = false;
while（startDate.isBefore（endDate））{
if（startDate.getDayOfWeek（）== DateTimeConstants.FRIDAY）{
fridays.add（startDate）;
达到AFriday = true;
}
if（reachedAFriday）{
startDate = startDate.plusWeeks（1）;
} else {
startDate = startDate.plusDays（1）;
}
}
I recently came across a task where i have to get all Fridays in a date range. I wrote a small piece of code and was surprised see some strange behaviour.
Below is my code:
public class Friday {
public static void main(String[]args){
String start = "01/01/2009";
String end = "12/09/2013";
String[] startTokens = start.split("/");
String[] endTokens = end.split("/");
Calendar startCal = new GregorianCalendar(Integer.parseInt(startTokens[2]),Integer.parseInt(startTokens[1])-1,Integer.parseInt(startTokens[0]));
Calendar endCal = new GregorianCalendar(Integer.parseInt(endTokens[2]),Integer.parseInt(endTokens[1])-1, Integer.parseInt(endTokens[0]));
int startYear = Integer.parseInt(startTokens[2]);
int endYear = Integer.parseInt(endTokens[2]);
int startWeek = startCal.get(Calendar.WEEK_OF_YEAR);
int endWeek = endCal.get(Calendar.WEEK_OF_YEAR);
Calendar cal = new GregorianCalendar();
cal.set(Calendar.DAY_OF_WEEK, Calendar.FRIDAY);
// cal.setMinimalDaysInFirstWeek(7);
ArrayList<String> main = new ArrayList<String>();
while(startYear <= endYear ){
cal.set(Calendar.YEAR, startYear);
System.out.println(cal.getMinimalDaysInFirstWeek());
if(startYear == endYear){
main.addAll(getFridays(startWeek, endWeek, cal));
}
else{
main.addAll(getFridays(startWeek, 52, cal));
startWeek = 1;
}
startYear =startYear +1;
}
for(String s: main){
System.err.println(s);
}
}
public static ArrayList<String> getFridays(int startWeek, int endWeek, Calendar cal){
ArrayList<String> fridays = new ArrayList<String>();
while(startWeek <= endWeek){
cal.set(Calendar.WEEK_OF_YEAR, startWeek);
fridays.add(cal.getTime().toString());
startWeek = startWeek+1;
}
return fridays;
}
}
Now when I ran the code i noticed that Fridays of 2011 are missing. After some debugging and online browsing i figured that Calendar.WEEK_OF_YEAR is locale specific and I have to use setMinimalDaysInFirstWeek(7) to fix it.
So uncommented the related line in the above code.
From what I understood now first week of year should start from full week of year.
For example Jan 1 2010 is friday. But it should not show up in results as i configured it to treat that week begins from Jan 3rd. But Now i still see the Jan 1 as friday
I am very much confused. Can some one explain why it is happening?
These Stackoverflow articles helped me a bit:
Why dec 31 2010 returns 1 as week of year?
Understanding java.util.Calendar WEEK_OF_YEAR
Here is an easier method, using the wonderful http://www.joda.org/joda-time/ library:
String start = "01/01/2009";
String end = "12/09/2013";
DateTimeFormatter pattern = DateTimeFormat.forPattern("dd/MM/yyyy");
DateTime startDate = pattern.parseDateTime(start);
DateTime endDate = pattern.parseDateTime(end);
List<DateTime> fridays = new ArrayList<>();
while (startDate.isBefore(endDate)){
if ( startDate.getDayOfWeek() == DateTimeConstants.FRIDAY ){
fridays.add(startDate);
}
startDate = startDate.plusDays(1);
}
at the end of this, you'd have the fridays in the fridays array. Simple?
Or if you want to speed things up, once you have gotten a friday, you can switch from using days, to using weeks:
String start = "01/01/2009";
String end = "12/09/2013";
DateTimeFormatter pattern = DateTimeFormat.forPattern("dd/MM/yyyy");
DateTime startDate = pattern.parseDateTime(start);
DateTime endDate = pattern.parseDateTime(end);
List<DateTime> fridays = new ArrayList<>();
boolean reachedAFriday = false;
while (startDate.isBefore(endDate)){
if ( startDate.getDayOfWeek() == DateTimeConstants.FRIDAY ){
fridays.add(startDate);
reachedAFriday = true;
}
if ( reachedAFriday ){
startDate = startDate.plusWeeks(1);
} else {
startDate = startDate.plusDays(1);
}
}
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