Develop Reference

How to add days and get timestamp in Android?

I want to add days like 30, 60, 90, etc to a date a timestamp like 1642599000000 and want to get the new timestamp. I am using the following code but not working properly. It only works for 30 days only.
Calendar c = Calendar.getInstance();
c.setTimeInMillis(initialTimestamp);
Date date= c.getTime();
Calendar cal = new GregorianCalendar();
cal.setTime(date);
cal.add(Calendar.DAY_OF_MONTH, 60); //Adding 60 days to current timestamp
long newTimestamp = cal.getTime().getTime(); //Required this

use c.add(Calendar.DATE, 60); instead DAY_OF_MONTH
DAY_OF_MONTH may be used for fetching number of day in current month (not year, not numer of all days fit into timestamp, which is huge and contains thousands of days)

Setting alarm android

I have a string that may contain value 07:00 or 11:00 0r 15:00
I want to set alarm for that time for today. it doesn't seem to work

One option is to create a calendar object set to midnight, and then offset it by the hours and minutes you have:
String alarm = "13:00";
Calendar c = new GregorianCalendar();
c.set(Calendar.HOUR_OF_DAY, 0);
c.set(Calendar.MINUTE, 0);
c.set(Calendar.SECOND, 0);
long millis = c.getTime().getTime();
millis += 1000*60*60*Integer.parseInt(alarm.substring(0, 2));
millis += 1000*60*Integer.parseInt(alarm.substring(3, 5));
Demo
An alternative to this would be to use two SimpleDateFormat masks to parse out the timestamp you want.

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.

In Android, how to create a Time value?

In my Android app, I'm using the Time class. I understand getting the current time like this:
Time now = new Time();
now.setToNow();
but what I'm stumbling on is how to create a set value of 8pm in the Time class. It's not just: Time time8 = "2200";, because that's a String, and Time time8 = 2200; is an integer. So I'm stumped.

There are multiple ways to that, I think the most easiest for you would be to just set it directly:
set(int second, int minute, int hour, int monthDay, int month, int year)
Calendar rightNow = Calendar.getInstance();
int day = rightNow.get(Calendar.DAY_OF_MONTH);
int month = rightNow.get(Calendar.MONTH);
int year = rightNow.get(Calendar.YEAR);
Time time8 = new Time();
time8.set(0,0,22,day,month,year);
But i would only do it like that if you really want to use Time otherwise Calendar is much more useful
Calendar calendar8= Calendar.getInstance();
calendar8.set(Calendar.SECOND, 0);
calendar8.set(Calendar.MINUTE, 0);
calendar8.set(Calendar.HOUR_OF_DAY,22);

Could use the calendar class
Calendar cal = Calendar.getInstance();
cal.set(Calendar.HOUR_OF_DAY,5);
cal.set(Calendar.MINUTE,50);
cal.set(Calendar.SECOND,0);
cal.set(Calendar.MILLISECOND,0);
Date d = cal.getTime();

From android Dev.
A specific moment in time, with millisecond precision. Values typically come from currentTimeMillis(), and are always UTC, regardless of the system's time zone. This is often called "Unix time" or "epoch time".
You can do Date instead of time
Date newdate = new Date();
You can use calendar to break it down to what you actually need.

Android timer - 1 hour incorrect

I hope someone can help. Im trying to set up a timer that times from the start of a game and displays this time. The problem is that the following section of code gives me the wrong time. Its in the wrong format, and is out by an hour.
private long startTime;
private SimpleDateFormat timeFormat = new SimpleDateFormat("HH:mm:ss.SS");
//Constructor:
startTime = System.currentTimeMillis();
public String getTime() {
long gameTime = System.currentTimeMillis() - startTime;
final Date date = new Date(gameTime);
return timeFormat.format(date);
}
It consistently gives me the output of 01:00:03:203. The seconds are correct, but the 1 hour shouldn't be there, and for format is 3 decimal places instead of the two I thought I specified.
Thank you very much!

Your date is epoch + gameTime. I think you're experiencing a daylight saving shift since the current DST in your location today doesn't match the DST at epoch.
Use a Calendar instead of a Date. Start with today and explicitly wipe out the hour, minute, etc. parts:
Calendar cal = Calendar.getInstance();
cal.set(Calendar.HOUR_OF_DAY, 0);
cal.set(Calendar.MINUTE, 0);
cal.set(Calendar.SECOND, 0);
cal.set(Calendar.MILLISECOND, 3600000 + 60000 + 1000 + 1);
SimpleDateFormat timeFormat = new SimpleDateFormat("HH:mm:ss.SS");
System.out.println(timeFormat.format(cal.getTime()));
The output for the above is: 01:01:01.01
http://ideone.com/DyQcl
Substitute the numbers I have above with gameTime and you're done.
Of course, this may not work once your millisecond ticks exceed the day boundary.