How do I convert day-of-the-year to date?

In the following example we want to get the date of the specified day-of-the-year. We can define a calendar for a specific day of the year by setting the java.util.Calendar object DAY_OF_YEAR field using the set() method. The method take the field to be set and a value.

package org.kodejava.example.util;

import java.util.Calendar;

public class DayOfYearToDate {
    public static void main(String[] args) {
        // In the example we want to get the date value of the specified
        // day of the year. Using the calendar object we can define our
        // calendar for a specific day of the year.
        int dayOfYear = 112;
        Calendar calendar = Calendar.getInstance();
        calendar.set(Calendar.DAY_OF_YEAR, dayOfYear);
        System.out.println("Day " + dayOfYear + " of the current year = "
                + calendar.getTime());

        // If you want to get the date for a specific day of year and for
        // a specific year, you can also pass the year information to the
        // calendar object.
        int year = 2020;
        calendar.set(Calendar.YEAR, year);
        System.out.println("Day " + dayOfYear + " in year " + year
                + " = " + calendar.getTime());
    }
}

And here is an example result of the code above:

Day 112 of the current year = Sat Apr 22 00:34:10 WITA 2017
Day 112 in year 2020 = Wed Apr 22 00:34:10 WITA 2020

How do I convert day-of-year to day-of-month?

package org.kodejava.example.util;

import java.util.Calendar;

public class DayYearToDayMonth {
    public static void main(String[] args) {
        // Create an instance of calendar for the year 2007 and set the
        // day to the 180 day of the year.
        Calendar cal = Calendar.getInstance();
        cal.set(Calendar.YEAR, 2007);
        cal.set(Calendar.DAY_OF_YEAR, 180);

        // Print the date of the calendar.
        System.out.println("Calendar date is: " + cal.getTime());

        // To know what day in month of the calendar we can obtain the
        // value by calling Calendar's instance get() method and pass
        // the Calendar.DAY_OF_MONTH field.
        int dayOfMonth = cal.get(Calendar.DAY_OF_MONTH);

        // Print which month day is it in number.
        System.out.println("Calendar day of month: " + dayOfMonth);

        // To know what day in week of the calendar we can obtain the
        // value by calling Calendar's instance get() method and pass
        // the Calendar.DAY_OF_WEEK field.
        int dayOfWeek = cal.get(Calendar.DAY_OF_WEEK);

        // Print which week day is it in number.
        System.out.println("Calendar day of week: " + dayOfWeek);
    }
}

The result of our above example is.

Calendar date is: Fri Jun 29 18:24:07 ICT 2007
Calendar day of month: 29
Calendar day of week: 6

How do I get day of week?

In this example we want to create a calendar / date from year and day of the year, because that’s all we have. Next we will find what is the day of week of the calendar object is. Let’s see the example below.

package org.kodejava.example.util;

import java.util.Calendar;

public class DayOfYearToDayOfWeekExample {
    public static void main(String[] args) {
        // Create a calendar with year and day of year.
        Calendar calendar = Calendar.getInstance();
        calendar.set(Calendar.YEAR, 2007);
        calendar.set(Calendar.DAY_OF_YEAR, 180);

        // See the full information of the calendar object.
        System.out.println(calendar.getTime().toString());

        // Get the weekday and print it
        int weekday = calendar.get(Calendar.DAY_OF_WEEK);
        System.out.println("Weekday: " + weekday);
    }
}

Below is the result of our program.

Fri Jun 29 17:16:22 ICT 2007
Weekday: 6