Returning Calendar with SimpleDateFormat

Question

I want to return the value of the calendar + 14 months using the SimpleDateFormat but am getting the below error.

private fun bestBeforeDate(cal: Calendar = Calendar.getInstance()): String
    {
        cal.add(Calendar.MONTH, 14)
        val format1 = SimpleDateFormat("dd-MM-yyy", Locale.getDefault()).format(this)
        return getString(R.string.best_before_date) + format1.format(cal)
    }

java.lang.IllegalArgumentException: Cannot format given Object as a Date

you can try with `add(Calender.YEAR,1) and add(Calender.MONTH,2). may be it works — Noshaf, Oct 22 '19 at 13:12
Then you should set Calendar year as +1 and month as +2, I can guide you better if you provide your expected String — Koushik Mondal, Oct 22 '19 at 13:12
Why are you passing this to the format method? That is what is causing the error. — jalynn2, Oct 22 '19 at 13:13
As an aside consider throwing away the long outmoded and notoriously troublesome `SimpleDateFormat` and friends, and adding [ThreeTenABP](https://github.com/JakeWharton/ThreeTenABP) to your Android project in order to use `java.time`, the modern Java date and time API. It is so much nicer to work with. — Ole V.V., Oct 22 '19 at 13:19
I am clearly overthinking this and confused myself. I just want the output string to be the return of the current date + 14 months. — Brummerly, Oct 22 '19 at 13:19

Ole V.V. · Answer 1 · 2019-10-22T14:19:24.143

java.time and ThreeTenABP

Sorry, I can write this in Java only. Please translate yourself. Your task is best solved using java.time, the modern Java date and time API.

    DateTimeFormatter dateFormatter = DateTimeFormatter.ofPattern("dd-MM-uuuu");
    LocalDate date = LocalDate.now(ZoneId.of("Europe/London")).plusMonths(14);
    String result = date.format(dateFormatter);
    System.out.println("Result: " + result);

Output when running today:

Result: 22-12-2020

Fixing your code

If you insist on using the notoriously troublesome and long outdated SimpleDateFormat class, just remove .format(this) from your code. I bet the exception is coming from there, and it’s wrong since you have an almost correct call to the format method in the following line.

private fun bestBeforeDate(cal: Calendar = Calendar.getInstance()): String
{
    cal.add(Calendar.MONTH, 14)
    val format1 = SimpleDateFormat("dd-MM-yyyy")
    return getString(R.string.best_before_date) + format1.format(cal.time)
}

The format method expects either a Date (another poorly designed and long outdated class) or a Long. Since this was neither of those, you got the exception.

Question: Doesn’t java.time require Android API level 26?

java.time works nicely on both older and newer Android devices. It just requires at least Java 6.

In Java 8 and later and on newer Android devices (from API level 26) the modern API comes built-in.
In non-Android Java 6 and 7 get the ThreeTen Backport, the backport of the modern classes (ThreeTen for JSR 310; see the links at the bottom).
On (older) Android use the Android edition of ThreeTen Backport. It’s called ThreeTenABP. And make sure you import the date and time classes from org.threeten.bp with subpackages.

Links

Oracle tutorial: Date Time explaining how to use java.time.
Java Specification Request (JSR) 310, where java.time was first described.
ThreeTen Backport project, the backport of java.time to Java 6 and 7 (ThreeTen for JSR-310).
ThreeTenABP, Android edition of ThreeTen Backport
Question: How to use ThreeTenABP in Android Project, with a very thorough explanation.

score 0 · Answer 2 · answered Oct 22 '19 at 13:41

    import java.util.Calendar;
import java.util.TimeZone;

/**
 * Java program to add, subtract dates, month and year using Calendar in Java.
 * Apart from date, Calendar class also provide time related information and can
 * be used to add and subtract hours, minutes and seconds from time in Java.
 *
 * @author Shahzad Ali
 */
public class DateAndTimeArithmetic {

    public static void main(String args[]){

        //Java calendar in default timezone and default locale
        Calendar cal = Calendar.getInstance();
        cal.setTimeZone(TimeZone.getTimeZone("GMT"));

        System.out.println("current date: " + getDate(cal));


        //adding days into Date in Java
        cal.add(Calendar.DATE, 2);
        System.out.println("date after 2 days : " + getDate(cal));

        //subtracting days from Date in Java
        cal.add(Calendar.DATE, -2);
        System.out.println("date before 2 days : " + getDate(cal));


       //adding moths into Date
        cal.add(Calendar.MONTH, 5);
        System.out.println("date after 5 months : " + getDate(cal));

        //subtracting months from Date
        cal.add(Calendar.MONTH, -5);
        System.out.println("date before 5 months : " + getDate(cal));

        //adding year into Date
        cal.add(Calendar.YEAR, 5);
        System.out.println("date after 5 years : " + getDate(cal));

        //subtracting year from Date
        cal.add(Calendar.YEAR, -5);
        System.out.println("date before 5 years : " + getDate(cal));

        //date after 200 days from now, takes care of how many days are in month
        //for years calendar takes care of leap year as well
        cal.add(Calendar.DATE, 200);
        System.out.println("date after 200 days from today : " + getDate(cal));

        System.out.println("current time in GMT: " + getTime(cal));

        //adding hours into Date
        cal.add(Calendar.HOUR_OF_DAY, 3);
        System.out.println("Time after 3 hours : " + getTime(cal));

        //subtracting hours from Date time
        cal.add(Calendar.HOUR_OF_DAY, -3);
        System.out.println("Time before 3 hours : " + getTime(cal));

        //adding minutes into Date time
        cal.add(Calendar.MINUTE, 3);
        System.out.println("Time after 3 minutes : " + getTime(cal));

        //subtracting minutes from Date time
        cal.add(Calendar.HOUR_OF_DAY, -3);
        System.out.println("Time before 3 minuets : " + getTime(cal));

    }

    /**
     *
     * @return current Date from Calendar in dd/MM/yyyy format
     * adding 1 into month because Calendar month starts from zero
     */
    public static String getDate(Calendar cal){
        return "" + cal.get(Calendar.DATE) +"/" +
                (cal.get(Calendar.MONTH)+1) + "/" + cal.get(Calendar.YEAR);
    }

    /**
     *
     * @return current Date from Calendar in HH:mm:SS format
     *
     * adding 1 into month because Calendar month starts from zero
     */
    public static String getTime(Calendar cal){
        return "" + cal.get(Calendar.HOUR_OF_DAY) +":" +
                (cal.get(Calendar.MINUTE)) + ":" + cal.get(Calendar.SECOND);
    }

}

Sample Output Should be like this: current date: 22/10/2019 date after 2 days : 22/10/2019 date before 2 days : 24/10/2019 date after 5 months : 22/3/2020

etc...

These terrible date-time classes were supplanted years ago by the *java.time* classes defined in JSR 310. See the modern solution in the [Answer by Ole V.V.](https://stackoverflow.com/a/58505299/642706) — Basil Bourque, Oct 22 '19 at 17:21

Returning Calendar with SimpleDateFormat

2 Answers2

java.time and ThreeTenABP

Fixing your code

Question: Doesn’t java.time require Android API level 26?

Links