Develop Reference

get start and end date of the week

Actually i want to display a set of data with the start and end date of the week were that particular date falls on. In my emulator its working fine. Eg. If i give Apr 23 its giving me start date of the week as 22 Apr and end date as 28 Apr, but if i try to build the same code in my device its showing start date of the week as 27 Apr and end date as 28 Apr.
Piece of Code which i am using:
//to get first day of week
cal1.set(Calendar.DAY_OF_WEEK, 1);
int day1 = cal1.get(Calendar.DAY_OF_MONTH);
//to get last day of week
cal1.set(Calendar.DAY_OF_WEEK, 7);
int day7 = cal1.get(Calendar.DAY_OF_MONTH);

I don't know why you getting that data but this is how I get the first and last date, take look might help. (its written to give current week's first and last date, so might have to tweak it little bit.)
Calendar calendar = Calendar.getInstance();
Date date1 = calendar.getTime();
//current date to check that our week lies in same month or not
SimpleDateFormat checkformate = new SimpleDateFormat("MM/yyyy");
String currentCheckdate= checkformate.format(date1);
int weekn = calendar.get(Calendar.WEEK_OF_MONTH);
int month = calendar.get(Calendar.MONTH);
int year = calendar.get(Calendar.YEAR);
//resat calender without date
calendar.clear();
calendar.setFirstDayOfWeek(Calendar.MONDAY);
calendar.set(Calendar.WEEK_OF_MONTH,weekn);
calendar.set(Calendar.MONTH,month);
calendar.set(Calendar.YEAR,year);
SimpleDateFormat simpleDateFormat = new SimpleDateFormat("dd/MM/yyyy");
Date datef = calendar.getTime();
//move date to 6 days + to get last date of week
Long timeSixDayPlus = calendar.getTimeInMillis()+518400000L;
Date dateL = new Date(timeSixDayPlus);
String firtdate = simpleDateFormat.format(datef);
String lastdate = simpleDateFormat.format(dateL);
String firtdateCheck = checkformate.format(datef);
String lastdateCheck = checkformate.format(dateL);
//if our week lies in two different months then we show only current month week part only
if (!firtdateCheck.toString().equalsIgnoreCase(currentCheckdate)) {
firtdate = "1" + "/" + calendar.get(Calendar.MONTH) + "/" + calendar.get(Calendar.YEAR);
}
if (!lastdateCheck.toString().equalsIgnoreCase(currentCheckdate)) {
int ma = calendar.getActualMaximum(Calendar.DAY_OF_MONTH);
lastdate = String.valueOf(ma) + "/" + calendar.get(Calendar.MONTH) + "/" + calendar.get(Calendar.YEAR);
}
Log.e("current","=>>"+firtdate+" to "+lastdate);

To get the first day of the week -
initialize the Calendar as per your need. in this case, I am getting the current date calendar.
set the current day of the week to the first day of the week.
get the corresponding date.
Calendar calendar = Calendar.getInstance();
//optional step
calendar.setFirstDayOfWeek(Calendar.SUNDAY);
calendar.set(Calendar.DAY_OF_WEEK, Calendar.SUNDAY);
int firstDateOfWeek = calendar.get(Calendar.DATE);
To get the last date of the week -
follow the step as above to initialize.
set the day of the week as Saturday.
get the corresponding date.
Calendar calendar = Calendar.getInstance();
//optional step
calendar.setFirstDayOfWeek(Calendar.SUNDAY);
calendar.set(Calendar.DAY_OF_WEEK, Calendar.SATURDAY);
int lastDateOfWeek = calendar.get(Calendar.DATE);
In this way, you can get eh first and the last date for the week. one thing to keep in mind that I have set the first day of the week as SUNDAY. set as per your need. although it is purely optional to set the first day of the week. this gives you a more transparency in code.

Android Formatter not giving correct time

so I have this code in Android
DateFormat formatter = new SimpleDateFormat("HH:mm", Locale.getDefault());
Calendar calendar = Calendar.getInstance();
calendar.setTimeInMillis(millisUntilFinished);
textView.setText(formatter.format(calendar.getTime()));
here is how I am passing the values to this method, where the hours and minutes strings are "8" and "30" for example
Calendar c = Calendar.getInstance();
String s = ApplicationPreferences.getWakeUp(ActivityStage1.this);
String[] separated = s.split("\\:");
String hours = separated[0];
String minutes = separated[1];
c.add(Calendar.DAY_OF_MONTH, 1);
c.set(Calendar.HOUR_OF_DAY, Integer.parseInt(hours));
c.set(Calendar.MINUTE, Integer.parseInt(minutes));
c.set(Calendar.SECOND, 0);
c.set(Calendar.MILLISECOND, 0);
long timeUntilStageTwo = (c.getTimeInMillis() - System.currentTimeMillis());
startStageTwoTimer(timeUntilStageTwo);
So the value in the long millisUntilFinished is something like 58441666, which is around 16 hours and 20 min, but for some reason the time it shows at the end in the text view is with 3 hours more, I even tried with different locales passed to SimpleDateFormat, and still the same, why is that happening?

Your Calendar c is in your local UTC+3 timezone while the system clock runs at UTC. Hence the difference of 3 hours.
You can use setTimeZone() to set an explicit timezone on your calendar before computing its millisecond value.
If you prefer to do the computations yourself, you can get the user's timezone with TimeZone.getDefault() and then use getOffset(time) to get the millisecond offset at specified UTC time.

How to add holidays in Android Calendar?

I am trying to add a list of holidays to my calendar. I am using the Caldroid library for displaying the calendar. I want to display a list of holidays in every month for which I need to select specific dates in every month. How do I do that ? The following is what I have tried:
CODE :
Calendar cal = Calendar.getInstance();
cal.add(Calendar.DATE, -18);
Date blueDate = cal.getTime();
cal = Calendar.getInstance();
cal.add(Calendar.DATE, 16);
int diff = cal.get(Calendar.JANUARY);
cal.add(diff, 10);
Date greenDate = cal.getTime();
I believed that diff would set the month to January and highlight the 11th of January cause I have given the value as 10 but it doesn't do so and I believe it is because I have instantiated the cal to getInstance() which would return the current month.
UPDATE :
Thanks to Meno, I have achieved the following but when I set the calendar to the second time, it takes only the updates value and does not set the first date (very obvious) but I want to know how to set multiple dates in a month without re-instantiating a new GregorianCalendar object for every month. Simply put, how do I set an array of dates in a month.
GregorianCalendar greg_cal = new GregorianCalendar();
greg_cal.set(Calendar.MONTH, Calendar.JANUARY);
greg_cal.set(Calendar.DAY_OF_MONTH, 1);
greg_cal.set(Calendar.MONTH, Calendar.JANUARY);
greg_cal.set(Calendar.DAY_OF_MONTH, 18);
Thanks in advance.

Your question does not appear to be clear. Nevertheless I try an answer. Instead of
cal = Calendar.getInstance(); // In Thailand this gives the buddhist calendar, do you want this?
cal.add(Calendar.DATE, 16); // 16 days from now, what is the intention or meaning???
cal.add(diff, 10); // first argument must be a defined constant in java.util.Calendar
I assume you just want to select a fixed date (as holiday). If so then you can call the set()-method and don't need to add days to move your calendar date forth and back:
GregorianCalendar cal = new GregorianCalendar(); // including currrent year
cal.set(Calendar.MONTH, Calendar.JANUARY);
cal.set(Calendar.DAY_OF_MONTH, 11);
Then you get as date the 11th of January in current year. By the way:
int diff = cal.get(Calendar.JANUARY);
This line is nonsense because:
Calendar.JANUARY is an int constant which is zero and denotes a value (the month) not a field. But the get(int)-method expects a field constant. The field constant with value zero corresponds to Calendar.ERA. Finally the line yields the era of cal, namely int diff = GregorianCalendar.AD = 1; assuming you use the gregorian calendar. This is surely not what you want???
UPDATED because of extra question in comment:
Reusing means that you don't create a new instance for the next calculation but reuse the same one (GregorianCalendar is mutable!). For example:
GregorianCalendar cal = new GregorianCalendar(); // including currrent year
cal.set(Calendar.MONTH, Calendar.JANUARY);
cal.set(Calendar.DAY_OF_MONTH, 11);
Date holiday1 = cal.getTime();
cal.set(Calendar.MONTH, Calendar.DECEMBER); // no new instance => reuse cal
cal.set(Calendar.DAY_OF_MONTH, 24);
Date holiday2 = cal.getTime();
...
I have also written about limiting to manipulations of month and day-of-month only because with manipulation of week-related fields the state of reused Calendar-instance depends on the order of field manipulations (very ugly and surprising).
Anyway, it is always safer to use immutable types which are available in Java 8 (not useable on Android), JodaTime and my alpha-state-library. I admit that the first contact with JodaTime can cause you feeling like lost because there are so many methods (the documentation standard is good for open-source but less good than for example in JSR-310). In your use-case I would use the type org.joda.time.LocalDate as start because you really have just a plain-date-use-case. Google and SO are your friends if you want to see more documentation beyond the original Joda documentation.
UPDATE due to extended question:
You have forgotten one important thing in your new code, namely to add the results of calendar setting to a holiday list, see here the modification:
List<Date> holidays = new ArrayList<Date>();
GregorianCalendar greg_cal = new GregorianCalendar();
greg_cal.set(Calendar.MONTH, Calendar.JANUARY);
greg_cal.set(Calendar.DAY_OF_MONTH, 1);
holidays.add(greg_cal.getTime());
greg_cal.set(Calendar.MONTH, Calendar.JANUARY);
greg_cal.set(Calendar.DAY_OF_MONTH, 18);
holidays.add(greg_cal.getTime());
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
for (Date d : holidays) {
System.out.println(sdf.format(d));
}
// output:
2014-01-01
2014-01-18
In an external library like JodaTime you would just use org.joda.time.LocalDate instead.
List<LocalDate> holidays = new ArrayList<LocalDate>();
LocalDate today = LocalDate.now();
holidays.add(today.withMonthOfYear(1).withDayOfMonth(1));
holidays.add(today.withMonthOfYear(1).withDayOfMonth(18));
It is pretty simple (similar in my unfinished date-and-time-library, too).

how to add no days to date object not calendar object

I have a Date object. Now I want to add days to that Date object.
So how that can be done? Actually using Calendar object that can be done I know.
But in my case, I haven't used a calendar objects. Instead only used date object.
For Example, suppose I have a date object
Date dtStartDate=o.getStartDate();
int x=28;
Now what I want to do is to add 28 to this date object, means if the dtStartDate is 1 July 2011
then after adding 28, dtStartDate will be 29 July 2011.
Please suggest it to me.
Thanks in advance

You can add Day using below
Calendar c1 = Calendar.getInstance();
c1.add(Calendar.DAY_OF_MONTH, 1);
Here 1 is number of Day you can add.
OR
Date dtStartDate=o.getStartDate();
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm");
Calendar c = Calendar.getInstance();
c.setTime(dtStartDate);
c.add(Calendar.DATE, 3); // number of days to add
String dt = sdf.format(c.getTime()); // dt is now the new date
Toast.makeText(this, "" + dt, 5000).show();
May be your problem solved.

You could add the equivilent number of milliseconds to the time retrieved from Date, e.g.:
long millis = dtStartDate.getTime();
millis = millis + x*24*60*60*1000;
Date dtEndDate = new Date();
dtEndDate.setTime(millis);

You can easily do this in two simple ways my friend. First one is:
Calendar cal = Calendar.getInstance();
cal.add(Calendar.DAY_OF_MONTH, 1);
and the second one is:
Calendar cal = Calendar.getInstance();
cal.add(Calendar.HOUR_OF_DAY, 24);
I think you would like to find this thing. Though there are so many persons are there who choose the first method.
Thanks.

Android Milliseconds as of a time

I have read all of the docs and there doesnt seem to be too much to really explains the date functions, or the lack there of.
I am trying implement the AlarmManger which needs the time in milliseconds (ms) for the trigger. To test I took the current time and added 5 seconds and that was good.
// get a Calendar object with current time
Calendar cal = Calendar.getInstance();
// add 5 minutes to the calendar object
cal.add(Calendar.SECOND, 5);
If I have a date and time how would I get the ms for that time.
Like "3/2/2011 08:15:00"
How do I turn that into milliseconds?

Use this method.
example:
method call for 3/2/2011 08:15:00
D2MS( 3, 2, 2011, 8, 15, 0);
method
public long D2MS(int month, int day, int year, int hour, int minute, int seconds) {
Calendar c = Calendar.getInstance();
c.set(year, month, day, hour, minute, seconds);
return c.getTimeInMillis();
}

When using AlarmManager you have two choices in setting an alarm - the first is time in ms since device reboot (don't understand that option) or, if you want an 'absolute' time, then you need to provide a UTC time in ms.
I think this should work - I've done something similar in the past...
public long getUtcTimeInMillis(String datetime) {
SimpleDateFormat sdf = new SimpleDateFormat("MM/dd/yyyy HH:mm:ss");
Date date = sdf.parse(datetime);
// getInstance() provides TZ info which can be used to adjust to UTC
Calendar cal = Calendar.getInstance();
cal.setTime(date);
// Get timezone offset then use it to adjust the return value
int offset = cal.getTimeZone().getOffset(cal.getTimeInMillis());
return cal.getTimeInMillis() + offset;
}
Personally I'd recommend trying to use a non-localised format such as yyyy-MM-dd HH:mm:ss for any date/time string you use if you want to cater for users globally.
The ISO 8601 international standard is yyyy-MM-dd HH:mm:ss.SSSZ but I don't normally go that far.