I am a novice to Java programming using Netbeans. I have added jCalendar to my GUI to pick a date.
I have entered this line in Events -> "property change" code of jCalendar button,
Date date=jcalendar1.getDate();
So that I get the date immediately when it is changed. Am I right?
The purpose:
I want to find the difference in milliseconds from the afternoon (12:00 pm) of this date above to NOW (current date and time).
There are several programs showing the date difference but all have dates hardcoded and being a newbie i do not know how to replace it with the date that is picked. (also i am confused between the objects Date and Calendar, not able to understand the difference between them). For example, a piece from here:
http://www.java2s.com/Code/Java/Data-type/ReturnsaDatesetjusttoNoontotheclosestpossiblemillisecondoftheday.htm
if (day == null) day = new Date();
cal.setTime(day);
cal.set(Calendar.HOUR_OF_DAY, 12);
cal.set(Calendar.MINUTE, cal.getMinimum(Calendar.MINUTE));
cal.set(Calendar.SECOND, cal.getMinimum(Calendar.SECOND));
cal.set(Calendar.MILLISECOND, cal.getMinimum(Calendar.MILLISECOND));
return cal.getTime();
Here day is a Date object. How is cal (a calendar object) linked to it to enter the time. How should the cal object be defined first? How can I use this or anything else in your opinion for my program. A piece of code with detail comments will be more helpful
thanks!
Instead of using :
Date day = new Date();
Use:
Calendar cal = Calendar.getInstance();
cal.set (...);
Date date = new Date(cal.getTimeInMillis());
Worth abstracting this stuff out to a DateUtils class or similar, with something like the following:
public static Date create(int year, int month, int day, int hour, int minute, int second) {
return new Date(getTimeInMillis(year, month, day, hour, minute, second));
}
public static long getTimeInMillis(int year, int month, int day, int hour, int minute, int second, int milliseconds) {
Calendar cal = Calendar.getInstance();
cal.clear();
cal.set(year, month, day, hour, minute, second);
cal.set(Calendar.MILLISECOND, milliseconds);
return cal.getTimeInMillis();
}
Related
I try to parse date string but always get wrong month. Here's my code.
This is code to select date from calender
#OnClick(R.id.tedit_tgllahir_addnew) void showTimeDialog(){
calendar = Calendar.getInstance();
year = calendar.get(Calendar.YEAR);
month = calendar.get(Calendar.MONTH);
date = calendar.get(Calendar.DAY_OF_MONTH);
DatePickerDialog datePickerDialog = new DatePickerDialog(AddDataForNewUserActivity.this,
new DatePickerDialog.OnDateSetListener() {
#Override
public void onDateSet(DatePicker view, int year, int month, int dayOfMonth) {
etTgl.setText(String.format("%02d/%02d/%02d", year, month+1, dayOfMonth));
}
}, year, month, date);
datePickerDialog.show();
}
and this is when i want to parse data
birth = LocalDate.of(list.getTglLahirAnak().getYear() + 1900, list.getTglLahirAnak().getMonth(), list.getTglLahirAnak().getDate());
int year = Period.between(birth, LocalDate.now()).getYears();
int month = Period.between(birth, LocalDate.now()).getMonths();
int totalBulan = year * 12 + month;
Whenever I input date from the calender, it always shows the wrong month. For example I choose May but in the system read April. Thanks to all who are willing to help.
I gather from your question that you are using the backport of JSR-310, probably the Android edition, ThreeTenABP. If so, go all-in on that and drop the use of the poorly designed and long outdated Calendar and Date classes.
Even if the use of the Date class is dictated from outside of your control, you must still stay away from its deprecated methods including getYear(), getMonth() and getDate(). You are trying the good thing when receiving a Date and converting it to a LocalDate first thing. Use DateTimeUtils from the backport for a first conversion.
But let’s take it from the top. Use LocalDate for setting the initial date of your date picker. Don’t use the old-fashioned Calendar class. I have not compiled the code, so please forgive if there’s a typo.
LocalDate today = LocalDate.now(ZoneId.systemDefault());
year = today.getYear();
month = today.getMonthValue(); // naturally 1-based
date = today.getDayOfMonth();
DatePickerDialog datePickerDialog = new DatePickerDialog(AddDataForNewUserActivity.this,
new DatePickerDialog.OnDateSetListener() {
#Override
public void onDateSet(DatePicker view, int year, int month, int dayOfMonth) {
// will return to this part later
}
}, year, month - 1, date); // Pass 0-based month
When the user selects a date from the calendar/date picker, don’t store it as a string. Store it as a LocalDate object. This saves you from doing any parsing later, and your code also shows that you need a LocalDate. Obviously if you want to show the selected date to the user, format the date into a string for that purpose (only). Use a DateTimeFormatter for formatting:
private static final DateTimeFormatter dateFormatter
= DateTimeFormatter.ofPattern("yy/MM/dd");
Now we go:
#Override
public void onDateSet(DatePicker view, int year, int month, int dayOfMonth) {
// Store the selected date somewhere you can find it later
selectedLocalDate = LocalDate.of(year, month + 1, dayOfMonth);
// Display to the user
String formattedDate = selectedLocalDate.format(dateFormatter);
etTgl.setText(formattedDate);
}
Now the calculation of age in months poses no problem anymore:
birth = selectedLocalDate;
long totalBulan = Period.between(birth, LocalDate.now(ZoneId.systemDefault()))
.toTotalMonths();
If you cannot control what you get from list.getTglLahirAnak(), the conversion from Date to LocalDate is:
Date oldfashionedDate = list.getTglLahirAnak();
birth = DateTimeUtils.toInstant(oldfashionedDate)
.atZone(ZoneId.systemDefault())
.toLocalDate();
Now the calculation of age proceeds as before.
What went wrong in your code?
Just like the outdated Calendar also the deprecated Date.getMonth() numbers the months from 0 for January through 11 for December. So if you pick a date in May, list.getTglLahirAnak().getMonth() returns 4 for May. When you feed this into a LocalDate with its natural and sensible month numbering, it gives you April.
Here I want to display dates like
2013-01-01,
2013-01-02,
2013-01-03,
.
.
...etc
I can get total days in a month
private int getDaysInMonth(int month, int year) {
Calendar cal = Calendar.getInstance(); // or pick another time zone if necessary
cal.set(Calendar.MONTH, month);
cal.set(Calendar.DAY_OF_MONTH, 1); // 1st day of month
cal.set(Calendar.YEAR, year);
cal.set(Calendar.HOUR, 0);
cal.set(Calendar.MINUTE, 0);
Date startDate = cal.getTime();
int nextMonth = (month == Calendar.DECEMBER) ? Calendar.JANUARY : month + 1;
cal.set(Calendar.MONTH, nextMonth);
if (month == Calendar.DECEMBER) {
cal.set(Calendar.YEAR, year + 1);
}
Date endDate = cal.getTime();
// get the number of days by measuring the time between the first of this
// month, and the first of next month
return (int)((endDate.getTime() - startDate.getTime()) / (24 * 60 * 60 * 1000));
}
Does anyone have an idea to help me?
If you only want to get the max number of days in a month you can do the following.
// Set day to one, add 1 month and subtract a day
Calendar cal = Calendar.getInstance();
cal.setTime(date);
cal.set(Calendar.DAY_OF_MONTH, 1);
cal.add(Calendar.MONTH, 1);
cal.add(Calendar.DAY_OF_MONTH, -1);
return cal.get(Calendar.DAY_OF_MONTH);
If you actually want to print every day then you can just set the day of month to 1 and keep adding a day in a loop until the month changes.
Calendar cal = Calendar.getInstance();
cal.setTime(date);
cal.set(Calendar.DAY_OF_MONTH, 1);
int myMonth=cal.get(Calendar.MONTH);
while (myMonth==cal.get(Calendar.MONTH)) {
System.out.print(cal.getTime());
cal.add(Calendar.DAY_OF_MONTH, 1);
}
Modern answer: Don’t use Calendar. Use java.time, the modern Java date and time API.
YearMonth ym = YearMonth.of(2013, Month.JANUARY);
LocalDate firstOfMonth = ym.atDay(1);
LocalDate firstOfFollowingMonth = ym.plusMonths(1).atDay(1);
firstOfMonth.datesUntil(firstOfFollowingMonth).forEach(System.out::println);
Output (abbreviated):
2013-01-01
2013-01-02
2013-01-03
…
2013-01-30
2013-01-31
datesUntil gives us a stream of dates until the specified end date exclusive, so when we give it the 1st of the following month, we get exactly all the dates of the month in question. In this example case up to and including January 31.
Link: Oracle tutorial: Date Time explaining how to use java.time.
This will give you all days of a month.
Calendar cal = Calendar.getInstance();
cal.set(Calendar.MONTH, 1);
cal.set(Calendar.DAY_OF_MONTH, 1);
int maxDay = cal.getActualMaximum(Calendar.DAY_OF_MONTH);
SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd");
System.out.print(df.format(cal.getTime()));
for (int i = 1; i < maxDay; i++) {
cal.set(Calendar.DAY_OF_MONTH, i + 1);
System.out.print(", " + df.format(cal.getTime()));
}
The first date is printed outside of loop for comma separated output.
A couple of comments...
Firstly, "... Calendar objects are particularly expensive to create." (J. Bloch, Effective Java, 2nd Ed.). If this is a method that you are going to be calling frequently, consider that you do not need to create a new Calendar object every time you call it.
Consider using a Calendar object held in a private static field that is initialized with a static initializer block. This presumes a single-threaded solution and would require synchronization in a concurrent environment. Otherwise, it really ought to be possible to reuse the same Calendar for your calculations.
Secondly, while you can find that greatest value for the DAY_OF_MONTH by iterating over the possible valid values, I think you can let the API do it for you. Consider using the getMaximum(DAY_OF_MONTH) or getGreatestMaximum(DAY_OF_MONTH) methods of the Calendar class.
Write a common method like that if you are using kotlin-
fun getAllDateOfMonth(year: Int, month: Month): List<LocalDate> {
val yearMonth= YearMonth.of(year, month)
val firstDayOfTheMonth = yearMonth.atDay(1)
val datesOfThisMonth = mutableListOf<LocalDate>()
for (daysNo in 0 until yearMonth.lengthOfMonth()){
datesOfThisMonth.add(firstDayOfTheMonth.plusDays(daysNo.toLong()))
}
return datesOfThisMonth
}
And call it like that -
getAllDateOfMonth(2021,Month.MAY):
I need to set some days in method set. I try to use:
c.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);
c.set(Calendar.DAY_OF_WEEK, Calendar.WEDNESDAY);
but with this way set only Wednesday.
Thank you and sorry for my english :)
The Calendar does not function as you expect it to. From the JavaDoc:
The Calendar class is an abstract class that provides methods for
converting between a specific instant in time and a set of calendar
fields such as YEAR, MONTH, DAY_OF_MONTH, HOUR, and so on, and for
manipulating the calendar fields, such as getting the date of the next
week. An instant in time can be represented by a millisecond value
that is an offset from the Epoch, January 1, 1970 00:00:00.000 GMT
(Gregorian).
Notice that the documentation states a specific instant in time. This implies the Calendar can only be based off of one point in time from epoch.
When you use the set method you are adjusting the specific instant in time through each call. So first it gets set to Monday then Wednesday.
You could use a List<Calendar> to store multiple Calendar instances set to your desired days.
public class CalendarTest {
public static void main(String[] args) {
Calendar cal1 = Calendar.getInstance();
Calendar cal2 = Calendar.getInstance();
cal1.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);
cal2.set(Calendar.DAY_OF_WEEK, Calendar.WEDNESDAY);
List<Calendar> calendars = Arrays.asList(cal1, cal2);
}
}
public static String getDay(String day,String month,String year){
int mm = Integer.parseInt(month);
int dd = Integer.parseInt(day);
int yy = Integer.parseInt(year);
LocalDate dt = LocalDate.of(yy, mm, dd);
return dt.getDayOfWeek().toString().toUpperCase();
}
I have Integer fields:
currentYear,currentMonth,currentDay,currentHour,currentMinute and nextYear,nextMonth,nextDay,nextHour,nextMinute.
How I can get difference between those two spots in time in milliseconds.
I found a way using Date() object, but those functions seems to be depricated, so it's little risky.
Any other way?
Use GregorianCalendar to create the date, and take the diff as you otherwise would.
GregorianCalendar currentDay=new GregorianCalendar (currentYear,currentMonth,currentDay,currentHour,currentMinute,0);
GregorianCalendar nextDay=new GregorianCalendar (nextYear,nextMonth,nextDay,nextHour,nextMinute,0);
diff_in_ms=nextDay. getTimeInMillis()-currentDay. getTimeInMillis();
Create a Calendar object for currenDay and nextDay, turn them into longs, then subtract. For example:
Calendar currentDate = Calendar.getInstance();
Calendar.set(Calendar.MONTH, currentMonth - 1); // January is 0, Feb is 1, etc.
Calendar.set(Calendar.DATE, currentDay);
// set the year, hour, minute, second, and millisecond
long currentDateInMillis = currentDate.getTimeInMillis();
Calendar nextDate = Calendar.getInstance();
// set the month, date, year, hour, minute, second, and millisecond
long nextDateInMillis = nextDate.getTimeInMillis();
return nextDateInMillis - currentDateInMillis; // this is what you want
If you don't like the confusion around the Calendar class, you can check out the Joda time library.
This mainly applies to android, but could be used in Java. I have these listeners:
int year, month, day, hour, minute;
// the callback received when the user "sets" the date in the dialog
private DatePickerDialog.OnDateSetListener mDateSetListener =
new DatePickerDialog.OnDateSetListener() {
public void onDateSet(DatePicker view, int year,
int monthOfYear, int dayOfMonth) {
year = year;
month = monthOfYear;
day = dayOfMonth;
}
};
// the callback received when the user "sets" the time in the dialog
private TimePickerDialog.OnTimeSetListener mTimeSetListener =
new TimePickerDialog.OnTimeSetListener() {
public void onTimeSet(TimePicker view, int hourOfDay, int minute) {
hour = hourOfDay;
minute = minute;
}
};
How could I convert int year, month, day, hour, minute; to a unix timestamp? Is this possible without the Date class?
Okay, use Calendar then, since that's preferred to Date anyway:
int componentTimeToTimestamp(int year, int month, int day, int hour, int minute) {
Calendar c = Calendar.getInstance();
c.set(Calendar.YEAR, year);
c.set(Calendar.MONTH, month);
c.set(Calendar.DAY_OF_MONTH, day);
c.set(Calendar.HOUR, hour);
c.set(Calendar.MINUTE, minute);
c.set(Calendar.SECOND, 0);
c.set(Calendar.MILLISECOND, 0);
return (int) (c.getTimeInMillis() / 1000L);
}
Calendar won't do any computations until getTimeMillis() is called and is designed to be more efficient than Date.
I'm assuming you want to avoid object overhead so I'm not suggesting any Date or Calendar classes; rather, you can calculate the value directly.
Unix time, or POSIX time, is a system for describing points in time, defined as the number of seconds elapsed since midnight Coordinated Universal Time (UTC) of January 1, 1970, not counting leap seconds. (Wikipedia article)
Calculate the number of days from Jan 1 1970 to the chosen year/month/day and multiply that by 24 * 3600, then add hour * 3600 + minute * 60 to get the number of seconds from 1970-01-01 00:00 to the chosen date and time.
There are well known algorithms for calculating the days between dates.
Since I wanted to account for daylight saving as well, along with local timezone, so after searching for hours all the possible solutions, what worked for me was as follows:
int gmtOffset = TimeZone.getDefault().getRawOffset();
int dstOffset = TimeZone.getDefault().getDSTSavings();
long unix_timestamp = (System.currentTimeMillis() + gmtOffset + dstOffset) / 1000;