below the lastDay variable does not always contain the i+1 of the list. No clue why. I am in the course of introducing the Date from Java 8. But still I would like to know what is going wrong... Peter (very beginner)
// organize the intervals and split them into the years
ArrayList<intervall> tmpIntervallList = new ArrayList<intervall>();
Calendar lastDay = Calendar.getInstance();
for (i = 0; i < deliveryList.size() - 1; i++) {
Log.d(TAG, "my log comments: Intervallanfang " +
deliveryList.get(i).getDatumasString() +" nächstes: " + deliveryList.get(i+1).getDatumasString());
//Beginning of the next intervall -1 is the last day of the Intervall before.
lastDay.set(deliveryList.get(i+1).getYear(),
deliveryList.get(i+1).getMonth(),
deliveryList.get(i+1).getDay());
//debugging
String tmp1String = String.format("%d/%d/%d", lastDay.get(Calendar.DAY_OF_MONTH),
lastDay.get(Calendar.MONTH) + 1,
lastDay.get(Calendar.YEAR));
Log.d(TAG, "my log comments: tmp lastday " + tmp1String );
lastDay.add(Calendar.DATE, -1);
//debugging
String tmpString = String.format("%d/%d/%d", lastDay.get(Calendar.DAY_OF_MONTH),
lastDay.get(Calendar.MONTH) + 1,
lastDay.get(Calendar.YEAR));
Log.d(TAG, "my log comments: ende intervall " + tmpString);
intervall tmp2intervall = new intervall(deliveryList.get(i).getAmountFilled(),
deliveryList.get(i).getYear(),
deliveryList.get(i).getMonth(),
deliveryList.get(i).getDay(),
lastDay.get(Calendar.YEAR),
lastDay.get(Calendar.MONTH),
lastDay.get(Calendar.DAY_OF_MONTH));
tmpIntervallList.add(tmp2intervall);
}
And the outcome is
my log comments: Intervallanfang 01/01/2018 nächstes: 01/02/2018
my log comments: tmp lastday 1/1/2018
my log comments: ende intervall 31/12/2017
my log comments: Intervallanfang 01/02/2018 nächstes: 01/06/2018
my log comments: tmp lastday 1/1/2018
my log comments: ende intervall 31/12/2017
my log comments: Intervallanfang 01/06/2018 nächstes: 01/01/2019
my log comments: tmp lastday 1/1/2019
my log comments: ende intervall 31/12/2018
my log comments: Intervallanfang 01/01/2019 nächstes: 01/01/2020
my log comments: tmp lastday 1/1/2020
my log comments: ende intervall 31/12/2019
my log comments: Intervallanfang 01/01/2020 nächstes: 01/06/2020
my log comments: tmp lastday 1/1/2020
my log comments: ende intervall 31/12/2019
my log comments: Intervallanfang 01/06/2020 nächstes: 02/01/2021
my log comments: tmp lastday 2/1/2021
my log comments: ende intervall 1/1/2021
as requested some more source code
public intervall(int amountFilled, int yearBegin, int monthBegin, int
dayBegin, int yearEnd, int monthEnd, int dayEnd) {
begin = Calendar.getInstance();
end = Calendar.getInstance();
this.setIntervall( yearBegin, monthBegin, dayBegin,
yearEnd, monthEnd, dayEnd);
this.amountFilled = amountFilled;
....
public void setIntervall(int amountFilled, int yearBegin, int
monthBegin, int dayBegin, int yearEnd, int monthEnd, int dayEnd){
this.begin.set(yearBegin, monthBegin, dayBegin);
this.end.set(yearEnd, monthEnd, dayEnd);
.....
this does not explain the strange behavior. As written I am in the course of introducing the Date from Java 8 but still I would like to understand.
Let’s just inspect the first two lines of your log output for a start:
my log comments: Intervallanfang 01/01/2018 nächstes: 01/02/2018 my log comments: tmp lastday 1/1/2018
(For readers who don’t read German: the first line means interval start 01/01/2018 next: 01/02/2018.)
The dates nächstes and tmp lastday come from the same element from your deliveryList, namely deliveryList.get(i+1). 01/02/2018 comes from getDatumasString() whereas 1/1/2018 comes from getYear(), getMonth() and getDay(). In the output you have correctly added 1 to the month number because the months are insanely numbered from 0 instead of 1 (probably a trait from the confusing GregorianCalendar class). So when these two dates do not agree, the problem must be inside whatever class those deliveries belong to. With the information you have provided, I don’t know what class that is, and even less what the problem in that class is (there was a reason why in a comment I encouraged you to create a Minimal, Reproducible Example).
There is a pattern, though: When we read your entire log output, nächstes and tmp lastday always agree on year and on day of month (even in the last iteration, where day of month is 2 for a change). And tmp lastday always gives month as 1 (January) no matter what it is in nächstes (2, 6 or 1). So it would seem that there’s a bug in getMonth() that causes it to return 0 (January) always irrespective of what is in the object.
Why getMonth() always returns January, it’s guesswork from me, but I dare start guessing. It might come from parsing the date string using SimpleDateFormat, a notorious troublemaker of a class. There are two typical errors that regularly cause it to return a date in January even though the input string is in a different month:
Y instead of lower case y for year in a format pattern string. See for example java parsing string to date.m for month. See for example SimpleDateFormat ignoring month when parsingIf any of these two turns out to fit your issue, I can almost guarantee you one thing: It would not have happened with java.time, the modern Java date and time API that Basil Bourque rightfully endorses in the other answer. java.time much better catches such errors long before you need to start debugging them.