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How do find day number(integer) of last day in the current month

I have specific date and i want to find last day number(integer) of month. I am using following code but always return current of date.
DateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
Date date = (Date) sdf.parse(year+"-"+(month<10?("0"+month):month)+"-01");
Calendar calendar = Calendar.getInstance();
calendar.setTime(date);
calendar.add(Calendar.MONTH, 1);
calendar.set(Calendar.DAY_OF_MONTH, 1);
calendar.add(Calendar.DATE, -1);
Date dt = (Date) calendar.getTime(); -> dt is return current date always
example: my date = 2018/04/30 and i want to find 30.
I couldnt find answer at site.
Thnx

If using Java 8 (or higher), don't use Calendar. If using Java 6 or 7, you might want to consider using the ThreeTen Backport. In either case, use the Java Time API.
Using Java Time
Since input is int year and int month, use YearMonth.
To find last day number of month, call lengthOfMonth().
To get the date at the end of month, call atEndOfMonth().
Demo
int year = 2020;
int month = 2;
int lastDay = YearMonth.of(year, month).lengthOfMonth();
System.out.println(lastDay);
LocalDate date = YearMonth.of(year, month).atEndOfMonth();
System.out.println(date);
Output
29
2020-02-29
Using Joda-Time
If you don't have Java 8, and already use Joda-Time, do it this way:
Demo
int year = 2020;
int month = 2;
int lastDay = new LocalDate(year, month, 1).dayOfMonth().getMaximumValue();
System.out.println(lastDay);
LocalDate date = new LocalDate(year, month, 1).dayOfMonth().withMaximumValue();
System.out.println(date);
Output
29
2020-02-29
Using Calendar
If you insist on using Calendar, call getActualMaximum(Calendar.DAY_OF_MONTH) as also mentioned in other answers.
Since input is int year and int month, don't build and parse a string, just set Calendar fields directly. Note that "month" in Calendar is zero-based.
Demo
int year = 2020;
int month = 2;
Calendar calendar = Calendar.getInstance();
calendar.clear();
calendar.set(year, month - 1, 1);
int lastDay = calendar.getActualMaximum(Calendar.DAY_OF_MONTH);
calendar.set(Calendar.DAY_OF_MONTH, lastDay);
Date date = calendar.getTime();
System.out.println(lastDay);
System.out.printf("%tF%n", date);
Output
29
2020-02-29

have specific date and i want to find last day number(integer) of month
getActualMaximum() is what you are looking for here.
Calendar cal = Calendar.getInstance();
cal.setTime(parsedDate);
cal.getActualMaximum(Calendar.DAY_OF_MONTH);

Calendar calendar =Calendar.getInstance();
calendar.set(Calendar.DATE, 1);
calendar.roll(Calendar.DATE, -1);
int lastDate=calendar.get(Calendar.DATE);

You can use calendar for that, like this:
calendar.getActualMaximum(Calendar.DAY_OF_MONTH);
Or, if you have joda, which is usually better:
DateTime d = new DateTame(dt);
d.dayOfMonth().getMaximumValue();

First, how are you getting the year to be used?
it should be simple by using Java Time LocalDate:
import java.time.*;
import static java.time.Month.*;
import static java.time.temporal.TemporalAdjusters.*;
import static java.time.temporal.ChronoField.*;
int lastDay = LocalDate.now() // or whatever date you want
.with(Month.of(yourMonth))
.with(lastDayOfMonth())
.get(DAY_OF_MONTH);
// or, if you have year and month, and want to find the corresponding last day
int lastDay = LocalDate.of(yourYear, yourMonth, 1)
.with(lastDayOfMonth())
.get(DAY_OF_MONTH);

How to reduce one month from current date and stored in date variable using java?

How to reduce one month from current date and want to sore in java.util.Date variable
im using this code but it's shows error in 2nd line
java.util.Date da = new Date();
da.add(Calendar.MONTH, -1); //error
How to store this date in java.util.Date variable?

Use Calendar:
Calendar cal = Calendar.getInstance();
cal.add(Calendar.MONTH, -1);
Date result = cal.getTime();

Starting from Java 8, the suggested way is to use the Date-Time API rather than Calendar.
If you want a Date object to be returned:
Date date = Date.from(ZonedDateTime.now().minusMonths(1).toInstant());
If you don't need exactly a Date object, you can use the classes directly, provided by the package, even to get dates in other time-zones:
ZonedDateTime dateInUTC = ZonedDateTime.now(ZoneId.of("Pacific/Auckland")).minusMonths(1);

Calendar calNow = Calendar.getInstance()
// adding -1 month
calNow.add(Calendar.MONTH, -1);
// fetching updated time
Date dateBeforeAMonth = calNow.getTime();

you can use Calendar
java.util.Date da = new Date();
Calendar cal = Calendar.getInstance();
cal.setTime(da);
cal.add(Calendar.MONTH, -1);
da = cal.getTime();

Using new java.time package in Java8 and Java9
import java.time.LocalDate;
LocalDate mydate = LocalDate.now(); // Or whatever you want
mydate = mydate.minusMonths(1);
The advantage to using this method is that you avoid all the issues about varying month lengths and have more flexibility in adjusting dates and ranges. The Local part also is Timezone smart so it's easy to convert between them.
As an aside, using java.time you can also get the day of the week, day of the month, all days up to the last of the month, all days up to a certain day of the week, etc.
mydate.plusMonths(1);
mydate.with(TemporalAdjusters.next(DayOfWeek.SUNDAY)).getDayOfMonth();
mydate.with(TemporalAdjusters.lastDayOfMonth());

Using JodaTime :
Date date = new DateTime().minusMonths(1).toDate();
JodaTime provides a convenient API for date manipulation.
Note that similar Date API will be introduced in JDK8 with the JSR310.

You can also use the DateUtils from apache common. The library also supports adding Hour, Minute, etc.
Date date = DateUtils.addMonths(new Date(), -1)

raduce 1 month of JDF
Date dateTo = new SimpleDateFormat("yyyy/MM/dd").parse(jdfMeTo.getJulianDate());
Calendar cal = Calendar.getInstance();
cal.setTime(dateTo);
cal.add(Calendar.MONTH, -1);
Date dateOf = cal.getTime();
Log.i("dateOf", dateOf.getTime() + "");
jdfMeOf.setJulianDate(cal.get(Calendar.DAY_OF_YEAR), cal.get(Calendar.DAY_OF_MONTH),
cal.get(Calendar.DAY_OF_WEEK_IN_MONTH));

Finding date before given number of months from a given date

I have a date say for e.g. current date which is 19/04/2013
And I have number of months given say for e.g. 10
I want to find out the date falling before 10 months from 19/04/2013.
How to achieve it in Java?
For example, if I want to find out date before a week, I can achieve as below:
Calendar calendar = Calendar.getInstance();
calendar.setTime(myDate);
calendar.add(Calendar.DAY_OF_YEAR, -7);
Date newDate = calendar.getTime();
But how to find the same for months ?

Well, you could do something similar to your example:
Calendar calendar = Calendar.getInstance();
calendar.setTime(myDate);
calendar.add(Calendar.MONTH, -10);
Date newDate = calendar.getTime();
It'll set newDate to a date 10 months before myDate.

Using jodatime this is so much easier and verbose:
LocalDate date = LocalDate.parse("19/04/2013", DateTimeFormat.forPattern("dd/MM/yyyy"));
LocalDate result = date.minus(Months.TEN);
System.out.println(result.toString("dd/MM/yyyy"));

How to subtract X day from a Date object in Java?

I want to do something like:
Date date = new Date(); // current date
date = date - 300; // substract 300 days from current date and I want to use this "date"
How to do it?

Java 8 and later
With Java 8's date time API change, Use LocalDate
LocalDate date = LocalDate.now().minusDays(300);
Similarly you can have
LocalDate date = someLocalDateInstance.minusDays(300);
Refer to https://stackoverflow.com/a/23885950/260990 for translation between java.util.Date <--> java.time.LocalDateTime
Date in = new Date();
LocalDateTime ldt = LocalDateTime.ofInstant(in.toInstant(), ZoneId.systemDefault());
Date out = Date.from(ldt.atZone(ZoneId.systemDefault()).toInstant());
Java 7 and earlier
Use Calendar's add() method
Calendar cal = Calendar.getInstance();
cal.setTime(dateInstance);
cal.add(Calendar.DATE, -30);
Date dateBefore30Days = cal.getTime();

#JigarJoshi it's the good answer, and of course also #Tim recommendation to use .joda-time.
I only want to add more possibilities to subtract days from a java.util.Date.
Apache-commons
One possibility is to use apache-commons-lang. You can do it using DateUtils as follows:
Date dateBefore30Days = DateUtils.addDays(new Date(),-30);
Of course add the commons-lang dependency to do only date subtract it's probably not a good options, however if you're already using commons-lang it's a good choice. There is also convenient methods to addYears,addMonths,addWeeks and so on, take a look at the api here.
Java 8
Another possibility is to take advantage of new LocalDate from Java 8 using minusDays(long days) method:
LocalDate dateBefore30Days = LocalDate.now(ZoneId.of("Europe/Paris")).minusDays(30);

Simply use this to get date before 300 days, replace 300 with your days:
Date date = new Date(); // Or where ever you get it from
Date daysAgo = new DateTime(date).minusDays(300).toDate();
Here,
DateTime is org.joda.time.DateTime;
Date is java.util.Date

Java 8 Time API:
Instant now = Instant.now(); //current date
Instant before = now.minus(Duration.ofDays(300));
Date dateBefore = Date.from(before);

As you can see HERE there is a lot of manipulation you can do. Here an example showing what you could do!
DateFormat dateFormat = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
Calendar cal = Calendar.getInstance();
//Add one day to current date.
cal.add(Calendar.DATE, 1);
System.out.println(dateFormat.format(cal.getTime()));
//Substract one day to current date.
cal = Calendar.getInstance();
cal.add(Calendar.DATE, -1);
System.out.println(dateFormat.format(cal.getTime()));
/* Can be Calendar.DATE or
* Calendar.MONTH, Calendar.YEAR, Calendar.HOUR, Calendar.SECOND
*/

With Java 8 it's really simple now:
LocalDate date = LocalDate.now().minusDays(300);
A great guide to the new api can be found here.

In Java 8 you can do this:
Instant inst = Instant.parse("2018-12-30T19:34:50.63Z");
// subtract 10 Days to Instant
Instant value = inst.minus(Period.ofDays(10));
// print result
System.out.println("Instant after subtracting Days: " + value);

I have created a function to make the task easier.
For 7 days after dateString: dateCalculate(dateString,"yyyy-MM-dd",7);
To get 7 days upto dateString: dateCalculate(dateString,"yyyy-MM-dd",-7);
public static String dateCalculate(String dateString, String dateFormat, int days) {
Calendar cal = Calendar.getInstance();
SimpleDateFormat s = new SimpleDateFormat(dateFormat);
try {
cal.setTime(s.parse(dateString));
} catch (ParseException e) {
e.printStackTrace();
}
cal.add(Calendar.DATE, days);
return s.format(cal.getTime());
}

You may also be able to use the Duration class. E.g.
Date currentDate = new Date();
Date oneDayFromCurrentDate = new Date(currentDate.getTime() - Duration.ofDays(1).toMillis());

You can easily subtract with calendar with SimpleDateFormat
public static String subtractDate(String time,int subtractDay) throws ParseException {
Calendar cal = Calendar.getInstance();
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm", Locale.ENGLISH);
cal.setTime(sdf.parse(time));
cal.add(Calendar.DATE,-subtractDay);
String wantedDate = sdf.format(cal.getTime());
Log.d("tag",wantedDate);
return wantedDate;
}

Take 3 Integers, create a date

I am trying to take 3 separate integer inputs (year,month,day) and taking these 3 entries and forming an object of date from them so I can use it to compare other dates.
This is what I have so far, at a loss at where to go from here:
public void compareDates() {
String dayString = txtOrderDateDay.getText();
String monthString = txtOrderDateMonth.getText();
String yearString = txtOrderDateYear.getText();
int day = Integer.parseInt(dayString);
int month = Integer.parseInt(monthString);
int year = Integer.parseInt(yearString);
}
Many thanks for any help you have to offer.

Try this, noticing that months start in zero so we need to subtract one to correctly specify a month:
Calendar calendar = Calendar.getInstance();
calendar.set(Calendar.YEAR, year);
calendar.set(Calendar.MONTH, month-1);
calendar.set(Calendar.DATE, day);
Date date = calendar.getTime();
Or this:
Calendar calendar = Calendar.getInstance();
calendar.set(year, month-1, day);
Date date = calendar.getTime();
Or this:
Date date = new GregorianCalendar(year, month-1, day).getTime();
The first method gives you more control, as it allows you to set other fields in the date, for instance: DAY_OF_WEEK, DAY_OF_WEEK_IN_MONTH, DAY_OF_YEAR, WEEK_OF_MONTH, WEEK_OF_YEAR, MILLISECOND, MINUTE, HOUR, HOUR_OF_DAY etc.
Finally, for correctly formatting the date as indicated in the comments, do this:
DateFormat df = new SimpleDateFormat("yyyy/MM/dd");
String strDate = df.format(date);

Use GregorianCalendar
new GregorianCalendar(int year, int month, int dayOfMonth)

Please refer to this library, in other to facilitate your life in such task - http://joda-time.sourceforge.net/
Then you are gonna write code like this:
LocalDate ld = new LocalDate(int year, int monthOfYear, int dayOfMonth) ;
This class offers a bunch of useful methods for comparison and operations like adding minutes... take a look at its documentation here
A bit more about joda-time:
Joda-Time provides a quality replacement for the Java date and time classes. The design allows for multiple calendar systems, while still providing a simple API. The 'default' calendar is the ISO8601 standard which is used by XML. The Gregorian, Julian, Buddhist, Coptic, Ethiopic and Islamic systems are also included, and we welcome further additions. Supporting classes include time zone, duration, format and parsing.