How to display time adding 30mins from current time

Question

I just want it to be displayed from current time adding 30mins till day ends Ex-Today time is 09:46AM It should display like 10:00AM,10:30AM,11:00AM....11:30PM for that particular date. But here in my code its displaying from 00:00...23:30 for whole day. Here is my code:

SimpleDateFormat df = new SimpleDateFormat("HH:mm");
        Calendar cal = Calendar.getInstance();
        cal.set(Calendar.HOUR_OF_DAY, 0);
        cal.set(Calendar.MINUTE, 0);
        cal.set(Calendar.SECOND, 0);
        int startDate = cal.get(Calendar.DATE);
        while (cal.get(Calendar.DATE) == startDate) {
            Log.d("time","currenttime"+cal.getTime());
            cal.add(Calendar.MINUTE, 30);
        }

Answer 1

java.time and ThreeTenABP

    Duration interval = Duration.ofMinutes(30);
    DateTimeFormatter timeFormatter = DateTimeFormatter.ofPattern("HH:mm");
    ZoneId zone = ZoneId.of("Europe/Podgorica");
    ZonedDateTime now = ZonedDateTime.now(zone);
    // Start at a whole half hour no earlier than now
    ZonedDateTime start = now.truncatedTo(ChronoUnit.HOURS);
    while (start.isBefore(now)) {
        start = start.plus(interval);
    }
    // End when a new day begins
    ZonedDateTime limit = now.toLocalDate().plusDays(1).atStartOfDay(zone);

    // Iterate
    ZonedDateTime currentTime = start;
    while (currentTime.isBefore(limit)) {
        System.out.println(currentTime.format(timeFormatter));
        currentTime = currentTime.plus(interval);
    }

When I ran the snippet just now, I got the following output:

20:30
21:00
21:30
22:00
22:30
23:00
23:30

Of course substitute your desired time zone where I put Europe/Podgorica.

I used the following imports:

import org.threeten.bp.Duration;
import org.threeten.bp.ZoneId;
import org.threeten.bp.ZonedDateTime;
import org.threeten.bp.format.DateTimeFormatter;
import org.threeten.bp.temporal.ChronoUnit;

Question: Can I use java.time on my Android API level?

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

• In Java 8 and later and on new Android devices (from API level 26) the modern API comes built-in. In this case import from java.time with subpackages (not org.threeten.bp).
• In Java 6 and 7 get the ThreeTen Backport, the backport of the new classes (ThreeTen for JSR 310, where the modern API was first described).
• On (older) Android, use the Android edition of ThreeTen Backport. It’s called ThreeTenABP. Make sure you import the date and time classes from package org.threeten.bp and subpackages.

Links

• Oracle tutorial: Date Time, explaining how to use java.time.
• ThreeTen Backport project
• ThreeTenABP, Android edition of ThreeTen Backport
• Question: How to use ThreeTenABP in Android Project, with a very thorough explanation.
• Java Specification Request (JSR) 310.

Answer 2

Use "HH:mm" for 24 hr format and "hh:mm a" for 12 hr format

Update 1

Below is a full example that displays what you want on a textview:

    TextView timeNow = findViewById(R.id.time_now);

    Calendar cal, atMidnight;

    //SimpleDateFormat df = new SimpleDateFormat("dd/MM/YYYY hh:mm a");
    SimpleDateFormat df = new SimpleDateFormat("hh:mm a");

    cal = Calendar.getInstance();
    atMidnight = Calendar.getInstance();

    atMidnight.add(Calendar.DATE, 1);
    atMidnight.set(Calendar.HOUR_OF_DAY, 0);
    atMidnight.set(Calendar.MINUTE, 0);
    atMidnight.set(Calendar.SECOND, 0);

    cal.add(Calendar.MINUTE, 30);

    String txt = "";

    while (cal.getTime().getTime() < atMidnight.getTime().getTime()) {
        txt = txt + df.format(cal.getTime()) + "\n";
        cal.add(Calendar.MINUTE, 30);
    }

    timeNow.setText(txt);

Update 2

To round the minutes to the next 30mins, you can do the below:

while (cal.getTime().getTime() < atMidnight.getTime().getTime()) {
    int unroundedMinutes = cal.get(Calendar.MINUTE);
    int mod = unroundedMinutes % 30;
    cal.add(Calendar.MINUTE, 30-mod);
    txt = txt + df.format(cal.getTime()) + "\n";
    cal.add(Calendar.MINUTE, 30);
    }

timeNow.setText(txt);