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How to get days in a month in Android

I have customer UI calendar I have an issue:
For example, September has 30 day start from 01/09/2020->30/09/2020 but UI calendar display from 29/08/2020->02/10/2020
This is my code. Who can help me?
val calendar: Calendar = Calendar.getInstance()
calendar.firstDayOfWeek = Calendar.MONDAY
calendar.add(Calendar.MONTH, position)
// Set day of month as 1
calendar.set(Calendar.DAY_OF_MONTH, 1)
// Get a number of the first day of the week
val dayOfWeek = calendar.get(Calendar.DAY_OF_WEEK)
// Count when month is beginning
val firstDayOfWeek = calendar.firstDayOfWeek
val monthBeginningCell = (if (dayOfWeek < firstDayOfWeek) 7 else 0) + dayOfWeek - firstDayOfWeek
// Subtract a number of beginning days, it will let to load a part of a previous month
calendar.add(Calendar.DAY_OF_MONTH, -monthBeginningCell)
/* Get all days of one page (35 is a number of all possible cells in one page
(a part of previous month, current month and a part of next month))
*/
while (days.size < 35) {
days.add(calendar.time)
calendar.add(Calendar.DAY_OF_MONTH, 1)
}

What are exactly you need? If you need full range of calendar for one month, you can use below code for example:
class Scratch {
public static void main(String[] args) {
Calendar calendar = Calendar.getInstance();
// The month you want to set
int month = Calendar.SEPTEMBER;
calendar.set(Calendar.MONTH, month);
int firstDayOfMonth = calendar.getActualMinimum(Calendar.DAY_OF_MONTH);
int lastDayOfMonth = calendar.getActualMaximum(Calendar.DAY_OF_MONTH);
System.out.println(getTimeOfWeek(lastDayOfMonth, false, month));
System.out.println(getTimeOfWeek(firstDayOfMonth, true, month));
}
private static Instant getTimeOfWeek(int day, boolean isFirst, int month) {
Calendar calendar = Calendar.getInstance();
calendar.set(Calendar.MONTH, month);
calendar.set(Calendar.DAY_OF_MONTH, day);
int dayInWeek = calendar.get(Calendar.DAY_OF_WEEK);
if (isFirst) {
calendar.set(Calendar.DAY_OF_MONTH, day - dayInWeek + 1);
} else {
calendar.set(Calendar.DAY_OF_MONTH, day + 7 - dayInWeek);
}
return calendar.toInstant();
}
}
If you only want the range on the month, just set the calendar to the first and the last day on that month.
Hope it works!

How to get last three months first date and last date based on current date including current date in java?

I want to categorize values based on months so to filter those values required 1st & last date of last three months based on current month including current month values. Here how many last months is parameter. I wanted list of all months 1st date and last date. Any logic for the same will be helpful.
for example:-
// parameters
int lastMonths = 3;
date currentDate= 26-04-2019;
//expected output
current month is 04-2019 ,1st date is 1-04-2019 and last date is 30-04-2019
previous month is 03-2019, 1st date is 01-03-2019 and last date is 31-03-2019
previous month is 02-2019, 1st date is 01-02-2019 and last date is 28-02-2019

Use java.util.Calendar for addition and subraction in date
and
java.text.DateFormat to format date
DateFormat format = new SimpleDateFormat("dd-MM-yyyy", Locale.US);
DateFormat monthFormat = new SimpleDateFormat("MM-yyyy", Locale.US);
Calendar cal = Calendar.getInstance();
cal.setTime(format.parse("26-04-2019"));
for (int i = 0; i < 3; i++){
System.out.println("currentDate: " + monthFormat.format(cal.getTime())); // print current month
cal.set(Calendar.DAY_OF_MONTH, 1);
System.out.println("first date: " + format.format(cal.getTime())); // print first date
cal.add(Calendar.MONTH, 1);
cal.set(Calendar.DAY_OF_MONTH, 1);
cal.add(Calendar.DATE, -1);
System.out.println("last date: " + format.format(cal.getTime())); // print last date
cal.add(Calendar.MONTH, -1);
}

Important to say - there are tons of libraries who will give you this specific need, but I would like relying on one that does the work and was actually designed for (some of yours...) those use cases -
Java.time.LocalDate library (already built into Java 8)
import java.time.LocalDate;
LocalDate now = LocalDate.now(); // 2019-04-26
In order to get first and last days of month, you can use:
LocalDate start = YearMonth.now().atDay(1);
(now can be some other month, of course)
LocalDate end = YearMonth.now().atEndOfMonth();
You can use it specifically on one / two months, or with some for loop. Examples below:
1. Specific call:
LocalDate earlierOneMonth = now.minusMonths(1); // 2019-03-26
earlierOneMonth.getDay(); // 26
2. For Loop: (so you'll need something like an array / list to store those values...)
for(int i=0; i < lastMonths - 1; i++){
arr(i) = now.minusMonths(i + 1);
}
Also, in order to get the name of the month, you can use ->
earlierOneMonth.getMonth(); // APRIL
earlierOneMonth.getMonth.getValue(); // 04
Lastly, in order to get the year, you can use ->
earlier.getYear(); // 2019
Once you have all of your desired values, you can print them out as you requested, with that expected output:
"current month is" + nowMonth + "-" + nowYear + " ,1st date is" + nowDay + "-" + nowMonth + "-" + nowYear + " and last date is ...
Let me know if it's clear enough :)

tl;dr
YearMonth.now().minusMonths( 3 ).atDay( 1 ) // Get the first day of the month of three months ago. Returns `LocalDate` object.
YearMonth.now().minusMonths( 3 ).atEndOfMonth() // Get the last day of the month of three months ago. Returns `LocalDate` object.
YearMonth
You really care about the months. The dates are secondary. So focus on the months. Java has a class for that!
The YearMonth class represents a particular month of a particular year.
ZoneId z = ZoneId.of( "America/Edmonton" ) ;
YearMonth currentYm = YearMonth.now( z ) ;
Collect your months of interest.
List< YearMonth > yms = new ArrayList<>() ;
int limit = 3 ; // We want current month plus three previous months.
for( int i = 0 ; i <= limit ; i ++ ) {
YearMonth ym = currentYm.minusMonths( i ) ;
yms.add( ym ) ;
}
When you need dates, loop the list. Let YearMonth determine the first and last days of the month.
for( YearMonth ym : yms ) {
System.out.println( "YearMonth: " + ym + " starts: " + ym.atDay( 1 ) + " ends: " + ym.atEndOfMonth() ) ;
}
See this code run live at IdeOne.com.
YearMonth: 2019-04 starts: 2019-04-01 ends: 2019-04-30
YearMonth: 2019-03 starts: 2019-03-01 ends: 2019-03-31
YearMonth: 2019-02 starts: 2019-02-01 ends: 2019-02-28
YearMonth: 2019-01 starts: 2019-01-01 ends: 2019-01-31

If you need a Date object then the following will do just fine
Date date = getDate(targetDate);
Calendar calendar = Calendar.getInstance();
calendar.setTime(date);
calendar.add(Calendar.MONTH, -3);
calendar.set(Calendar.DAY_OF_MONTH, 1);
// calendar.getTime()
// The line above returns Date object
If you need a plain String then you can format it any way you want by simply using DateTimeFormatter from org.joda.time library and just use it's print() method on calendar.getTimeInMillis().

LocalDate currentDate = LocalDate.of(2019, 4, 26);//current date
System.out.println(currentDate);
int lastMonths = 3;//number of months
LocalDate prevDate = null;
LocalDate start = null;
LocalDate end = null;
for(int i = 0; i < lastMonths; i++) {
if(prevDate == null) {
start = currentDate.withDayOfMonth(1);//First day of current month
end = currentDate.withDayOfMonth(currentDate.lengthOfMonth());//Last day of current month
prevDate = currentDate.minusMonths(1);//subtracting one month from current month
} else {
start = prevDate.withDayOfMonth(1);//First day of previous month
end = prevDate.withDayOfMonth(prevDate.lengthOfMonth());//Last day of previous month
prevDate = prevDate.minusMonths(1);//subtracting one month from previous month
}
System.out.println(start + " " + end);
}
Output:
2019-04-26
2019-04-01 2019-04-30
2019-03-01 2019-03-31
2019-02-01 2019-02-28
Reference:
Get first and last day of month using threeten, LocalDate

int lastMonths = 3;
Calendar calendar = Calendar.getInstance();
int year = calendar.get(Calendar.YEAR);
int month = calendar.get(Calendar.MONTH) + 1;
int dayOfMonth = calendar.get(Calendar.DAY_OF_MONTH);
DateFormat monthYearFormat = new SimpleDateFormat("MM-yyyy");
for (int i = 0; i < lastMonths; i++) {
int monthOfYear = month - i;
// if month is january, reset couter and month
if(monthOfYear == 0) {
month = 13;
year -= 1;
i = 0;
continue;
}
// get last day of month (month length)
YearMonth yearMonth = YearMonth.of(year, monthOfYear);
int firstDay = 1;
int lastDay = yearMonth.lengthOfMonth();
// create date with given year, month and day
Date date = new GregorianCalendar(year, monthOfYear - 1, firstDay).getTime();
String monthAndYear = monthYearFormat.format(date);
String currentOrPrevious;
if (i == 0) {
currentOrPrevious = "current";
} else {
currentOrPrevious = "previous";
}
String output = String.format("%s month is %s, 1st date is %02d-%s and last date is %d-%s", currentOrPrevious, monthAndYear, firstDay, monthAndYear, lastDay, monthAndYear);
System.out.println(output);
}
Output:
current month is 04-2019, 1st date is 01-04-2019 and last date is 30-04-2019
previous month is 03-2019, 1st date is 01-03-2019 and last date is 31-03-2019
previous month is 02-2019, 1st date is 01-02-2019 and last date is 28-02-2019

How do I print out a calendar month in console?

I have an assignment for a class I'm taking in which I have to make a Java console application, and it involves asking the user for a date, parsing that date, and working out what day of the month that date starts on. I have to then print out a calendar to look like this:
Calendar for September 2016
Su Mo Tu We Th Fr Sa
- - - - 1 2 3
4 5 6 7 8 9 10
11 12 13 14 15 16 17
18 19 20 21 22 23 24
25 26 27 28 29 30 -
I have the date, I have the number of the day that the date starts on, (eg. Day= 1 (Monday), Day= 2(Tuesday), etc.)
Now, I can use a very messy looking switch statement with nested if statements that says, depending on the value of Day, and the number of days in that month, print out this pre-made calendar, and I can just pre-make a calendar for every eventual combination of Day and number of days in that month. But I don't want to do that, and I can't figure out an easier way of doing it. Has anybody got any ideas of a tidier, more succinct way of doing it? Would it be something involving 2d arrays?
PS. I'm not allowed to use any date-based library classes available in Java.

well you can use this if you change your mind
public static void main(String args [])
{
// type MM yyyy
Scanner in = new Scanner(System.in);
System.out.print("Enter month and year: MM yyyy ");
int month = in.nextInt();
int year = in.nextInt();
in.close();
// checks valid month
try {
if (month < 1 || month > 12)
throw new Exception("Invalid index for month: " + month);
printCalendarMonthYear(month, year);}
catch (Exception e) {
System.err.println(e.getMessage());
}
}
private static void printCalendarMonthYear(int month, int year) {
Calendar cal = new GregorianCalendar();
cal.clear();
cal.set(year, month - 1, 1); // setting the calendar to the month and year provided as parameters
System.out.println("Calendar for "+ cal.getDisplayName(Calendar.MONTH, Calendar.LONG,
Locale.US) + " " + cal.get(Calendar.YEAR));//to print Calendar for month and year
int firstWeekdayOfMonth = cal.get(Calendar.DAY_OF_WEEK);//which weekday was the first in month
int numberOfMonthDays = cal.getActualMaximum(Calendar.DAY_OF_MONTH); //lengh of days in a month
printCalendar(numberOfMonthDays, firstWeekdayOfMonth);
}
private static void printCalendar(int numberOfMonthDays, int firstWeekdayOfMonth) {
int weekdayIndex = 0;
System.out.println("Su MO Tu We Th Fr Sa"); // The order of days depends on your calendar
for (int day = 1; day < firstWeekdayOfMonth; day++) {
System.out.print(" "); //this loop to print the first day in his correct place
weekdayIndex++;
}
for (int day = 1; day <= numberOfMonthDays; day++) {
if (day<10) // this is just for better visialising because unit number take less space of course than 2
System.out.print(day+" ");
else System.out.print(day);
weekdayIndex++;
if (weekdayIndex == 7) {
weekdayIndex = 0;
System.out.println();
} else {
System.out.print(" ");
}}}

create a calendar of any year in ms word file using java [closed]

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I am trying to create calendar of any year in ms word file using java.could you please help me out.thanks in advance.

Following is the code to write calender for particular year in docx file
import java.util.Calendar;
import java.util.GregorianCalendar;
import java.util.Locale;
import java.util.Scanner;
import java.io.File;
import java.io.FileOutputStream;
import org.apache.poi.xwpf.usermodel.XWPFDocument;
import org.apache.poi.xwpf.usermodel.XWPFTable;
import org.apache.poi.xwpf.usermodel.XWPFTableRow;
public class MyCalendar {
//Blank Document
static XWPFDocument document= new XWPFDocument();
public static void main(String[] args) {
// represents the year
int year;
// ask year from user
Scanner in = new Scanner(System.in);
System.out.print("Enter year: ");
// read them as string
String yearText = in.next();
in.close();
try {
//Write the Document in file system
FileOutputStream out = new FileOutputStream(new File("Year "+yearText+".docx"));
// throws NumberFormatException if not convertible.
// It would be caught below:
year = Integer.parseInt(yearText);
// print the calendar for the given year.
for(int i=1; i<=12; i++){
printCalendarMonthYear(i, year);
}
document.write(out);
out.close();
} catch (NumberFormatException e) {
// handles NumberFormatException
System.err.println("Numberat Error: " + e.getMessage());
} catch (Exception e) {
// handles any other Exception
System.err.println(e.getMessage());
}
}
/*
* prints a calendar month based on month / year info
*/
private static void printCalendarMonthYear(int month, int year) {
// create a new GregorianCalendar object
Calendar cal = new GregorianCalendar();
// set its date to the first day of the month/year given by user
cal.clear();
cal.set(year, month - 1, 1);
document.createParagraph().createRun().setText(""+cal.getDisplayName(Calendar.MONTH, Calendar.LONG,
Locale.US) + " " + cal.get(Calendar.YEAR));
// obtain the weekday of the first day of month.
int firstWeekdayOfMonth = cal.get(Calendar.DAY_OF_WEEK);
// obtain the number of days in month.
int numberOfMonthDays = cal.getActualMaximum(Calendar.DAY_OF_MONTH);
// print anonymous calendar month based on the weekday of the first
// day of the month and the number of days in month:
printCalendar(numberOfMonthDays, firstWeekdayOfMonth-1);
}
/*
* prints an anonymous calendar month based on the weekday of the first
* day of the month and the number of days in month:
*/
private static void printCalendar(int numberOfMonthDays, int firstWeekdayOfMonth) {
// reset index of weekday
int weekdayIndex = 0;
// print calendar weekday header
XWPFTable table = document.createTable();
//create first row
XWPFTableRow tableRowOne = table.getRow(0);
tableRowOne.getCell(0).setText("Su");
tableRowOne.addNewTableCell().setText("Mo");
tableRowOne.addNewTableCell().setText("Tu");
tableRowOne.addNewTableCell().setText("We");
tableRowOne.addNewTableCell().setText("Th");
tableRowOne.addNewTableCell().setText("Fr");
tableRowOne.addNewTableCell().setText("Sa");
// leave/skip weekdays before the first day of month
XWPFTableRow tableRow = table.createRow();
int ind = 0;
for (int day = 1; day <= firstWeekdayOfMonth; day++) {
ind = day;
tableRow.getCell(ind).setText(" ");
weekdayIndex++;
}
// print the days of month in tabular format.
for (int day = 1; day <= numberOfMonthDays; day++) {
// print day
tableRow.getCell(ind).setText(""+day);
// next weekday
weekdayIndex++;
// if it is the last weekday
if (weekdayIndex == 7) {
// reset it
weekdayIndex = 0;
// and go to next line
tableRow = table.createRow();
ind = 0;
}
else { // otherwise
// print space
ind++;
}
}
// print a final new-line.
document.createParagraph().createRun().addBreak();
}
}
This will create docx file with year name
You will need following jar files to run this code
poi-3.11.jar
poi-ooxml-3.11.jar
poi-ooxml-schemas-3.11.jar
xmlbeans-2.6.jar

Java code to determine number of days elapsed does not return correct answer

The problem with this code is that it does calculate the days alive only for some birth dates. I tried using different birth dates and testing it with an online calculator and it seems not all are correct. I think the problem is because of Leapyears, more and less than 30 days in a month.
public class DaysAlive {
public static void main (String [] args){
Scanner userInput = new Scanner(System.in);
int TodayYear, TodayMonth, TodayDay;
int YearBorn, MonthBorn, DayBorn;
int DaysAlive;
System.out.println("Enter today's date");
System.out.print ("Year: ");
TodayYear = userInput.nextInt ();
System.out.print ("Month: ");
TodayMonth = userInput.nextInt ();
System.out.print ("Day: ");
TodayDay = userInput.nextInt ();
System.out.println("Enter date of birth");
System.out.print ("Year: ");
YearBorn = userInput.nextInt ();
System.out.print ("Month: ");
MonthBorn = userInput.nextInt ();
System.out.print ("Day: ");
DayBorn = userInput.nextInt ();
//I think this line is the problem
DaysAlive = (TodayYear - YearBorn) *365 + (TodayMonth - MonthBorn) *30 +(TodayDay - DayBorn);
System.out.println("DaysAlive: " + DaysAlive);
}
}

How about using Calendar? It will do all of that for you... or joda time library
check it out here:
Getting the number of days between two dates in java

If I understand what you want, you should be able to use something like this -
public static void main(String[] args) {
Scanner userInput = new Scanner(System.in);
System.out.println("Enter today's date");
System.out.print("Year: ");
int todayYear = userInput.nextInt();
System.out.print("Month: ");
int todayMonth = userInput.nextInt();
System.out.print("Day: ");
int todayDay = userInput.nextInt();
// Java has January as month 0. Let's not require that the user know.
Calendar today = new GregorianCalendar(todayYear, todayMonth - 1,
todayDay);
System.out.println("Enter date of birth");
System.out.print("Year: ");
int yearBorn = userInput.nextInt();
System.out.print("Month: ");
int monthBorn = userInput.nextInt();
System.out.print("Day: ");
int dayBorn = userInput.nextInt();
Calendar born = new GregorianCalendar(yearBorn, monthBorn - 1, dayBorn);
double diff = today.getTimeInMillis() - born.getTimeInMillis();
diff = diff / (24 * 60 * 60 * 1000); // hours in a day, minutes in a hour,
// seconds in a minute, millis in a
// second.
System.out.println(Math.round(diff));
}
With output
Enter today's date
Year: 2014
Month: 03
Day: 14
Enter date of birth
Year: 2014
Month: 03
Day: 13
1

You are right, the problem is that not all months have 30 days in them. A simple solution would to be use if statements and make another integer variable called something like monthMultiplier. As other people pointed out you can also use the Calendar
if(TodayMonth == 9 || TodayMonth == 11 || TodayMonth == 4 || TodayMonth == 6) {
monthMultiplier = 30;//30 days in these months
}
if(TodayMonth == 2){
monthMultiplier = 28;//WELL 28.25 accounting for leap years
}
else {
monthMultiplier = 31;
}
DaysAlive = (TodayYear - YearBorn) *365 + (TodayMonth - MonthBorn) * monthMultiplier +(TodayDay - DayBorn);

Joda-Time
The Joda-Time library makes easy work of this problem. Just one line of code, basically. Joda-Time handles time zones, leap days, and other issues.
Hand-coding such date-time work is risky, error-prone, and frankly silly given the excellent libraries available (Joda-Time and the new java.time package in Java 8).
Example Code
Here’s some example code in Joda-Time 2.3.
DateTimeZone timeZone = DateTimeZone.forID( "Europe/Paris" );
DateTime start = new DateTime(2008, 4, 26, 0, 0, 0, timeZone);
DateTime stop = new DateTime(2008, 5, 26, 0, 0, 0, timeZone);
int daysBetween = Days.daysBetween( start, stop ).getDays();
Dump to console…
System.out.println( "start: " + start );
System.out.println( "stop: " + stop );
System.out.println( "daysBetween: " + daysBetween );
When executed…
start: 2008-04-26T00:00:00.000+02:00
stop: 2008-05-26T00:00:00.000+02:00
daysBetween: 30