add seconds to System.currentTimeMills()

Question

I am trying to calculate the time of 100 days from now using the following:

import java.util.Date;
public class Main
{
    public static void main(String[] args) {
        System.out.println("Hello World");
        System.out.println(new Date(System.currentTimeMillis() + 8640000 * 1000));
    }
}

It gives me back Jan 04 08:57:25 UTC 2021 which is not correct. How should I remedy this?

Integer overflow. 8640000×1000 > 2³¹. Change `8640000` to `8640000L` so Java knows you’re doing math with 64-bit `long` values, which will not overflow. — VGR, Jan 03 '21 at 19:13
Also consider `LocalDateTime.now().plus(Duration.ofDays(100))`. — trashgod, Jan 03 '21 at 19:23
@trashgod Why `plus(Duration.ofDays(100))` when `plusDays(100)` is available? — Andreas, Jan 03 '21 at 20:31
While in UTC 100 days equals the number of milliseconds you try to calculalte, in very many other time zones it often is not the case since a day may be for example 23 or 25 hours. — Ole V.V., Jan 03 '21 at 22:16
@Andreas: Good question; I started to go that way, but I wanted to emphasize the notion of `Duration`. — trashgod, Jan 04 '21 at 13:31
Does this answer your question? [Android Days between two dates](https://stackoverflow.com/questions/23323792/android-days-between-two-dates). [This](https://stackoverflow.com/questions/49776292/why-is-this-not-casting-to-long)? — Ole V.V., Jan 05 '21 at 02:43

score 5 · Accepted Answer · answered Jan 03 '21 at 19:25

Use the following:

System.out.println(new Date(System.currentTimeMillis() + (long)8640000 * 1000));

Or

System.out.println(new Date(System.currentTimeMillis() + 8640000L * 1000));

8640000 * 1000 is 8,640,000,000, which exceeds Integer.MAX_VALUE of 2,147,483,647. You can solve this issue by casting it to a long.

This gives the result:

Tue Apr 13 15:26:10 EDT 2021

Arvind Kumar Avinash · Answer 2 · 2021-01-03T21:01:10.453

The date-time API of java.util and their formatting API, SimpleDateFormat are outdated and error-prone. It is recommended to stop using them completely and switch to the modern date-time API.

For any reason, if you have to stick to Java 6 or Java 7, you can use ThreeTen-Backport which backports most of the java.time functionality to Java 6 & 7.
If you are working for an Android project and your Android API level is still not compliant with Java-8, check Java 8+ APIs available through desugaring and How to use ThreeTenABP in Android Project.

Using the modern API:

import java.time.LocalDate;
import java.time.ZoneId;

public class Main {
    public static void main(String[] args) {
        // Change the ZoneId as per your requirement e.g. ZoneId.of("Europe/London")
        LocalDate today = LocalDate.now(ZoneId.systemDefault());
        LocalDate after100Days = today.plusDays(100);
        System.out.println(after100Days);
    }
}

Output:

2021-04-13

Learn about the modern date-time API from Trail: Date Time.

Using the legacy API:

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

public class Main {
    public static void main(String[] args) {
        // Change the TimeZone as per your requirement e.g. TimeZone.getTimeZone("Europe/London")
        Calendar calendar = Calendar.getInstance(TimeZone.getDefault());
        calendar.add(Calendar.DAY_OF_YEAR, 100);
        Date after100Days = calendar.getTime();
        System.out.println(after100Days);
    }
}

Output:

Tue Apr 13 19:40:11 BST 2021

Technical 101 · Answer 3 · 2021-01-04T08:48:18.690

3

Try sometime like

LocalDateTime.now().plusDays(100).toString()

or

SimpleDateFormat sdf = new SimpleDateFormat("dd MMM yyyy HH:mm:ss z"); // you could used any format
Calendar c = Calendar.getInstance();
c.add(Calendar.DATE, 100); // Adding 100 days
String output = sdf.format(c.getTime());
System.out.println(output);

edited Jan 04 '21 at 08:48

answered Jan 03 '21 at 19:25

Technical 101

138
7

1

`c.setTime(new Date());` is redundant, since the `Calendar` object returned by [`getInstance()`](https://docs.oracle.com/javase/8/docs/api/java/util/Calendar.html#getInstance--) is already the current time: *"Gets a calendar using the default time zone and locale. The **Calendar returned is based on the current time** in the default time zone with the default FORMAT locale."* – Andreas Jan 03 '21 at 20:33
Yes you are right, Just added it incase you want to reset the date. I have edited it – Technical 101 Jan 04 '21 at 08:48

add seconds to System.currentTimeMills()

3 Answers3