Date d = Calendar.getTime() returns wrong time?

Question

Calendar calendar = Calendar.getInstance();
calendar.set(calendar.HOUR, 8);
calendar.set(calendar.MINUTE, 45);
calendar.set(calendar.SECOND, 00);
    
Date d = calendar.getTime();
    
System.out.println(d);

Output is: Wed Oct 05 20:45:00 BST 2011

Can anyone help me with why this is?

Answer 1

Calendar.HOUR is used to set the hour as set on a 12-hour clock.

In other words, you do set the Calendar to 20:45. It's 8:45 PM.

Use Calendar.HOUR_OF_DAY to set the 24-hour-clock value.

Answer 2

Sure - you're setting Calendar.HOUR which represents the 1-12 "hour of half day". You should be using HOUR_OF_DAY which is the 0-23 value for the whole day:

calendar.set(Calendar.HOUR_OF_DAY, 8);

Alternatively, use Joda Time which is a much nicer date/time API :)

As an aside, please don't refer to static members via references... it will lead to pain when you call someOtherThread.sleep(...) and your current thread sleeps...

Answer 3

java.time

The java.util Date-Time API and their formatting API, SimpleDateFormat are outdated and error-prone.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^*.

Solution using java.time, the modern Date-Time API:

import java.time.Instant;
import java.time.OffsetDateTime;
import java.time.ZoneOffset;

public class Main {
    public static void main(String[] args) {
        Instant instant = OffsetDateTime.now(ZoneOffset.UTC)
                            .withHour(8)
                            .withMinute(45)
                            .withSecond(0)
                            .toInstant();
        System.out.println(instant);
    }
}

ONLINE DEMO

An Instant represents an instantaneous point on the timeline in UTC. The Z in the output is the timezone designator for a zero-timezone offset. It stands for Zulu and specifies the Etc/UTC timezone (which has the timezone offset of +00:00 hours).

For any reason, if you need to convert this object of Instant to an object of java.util.Date, you can do so as follows:

Date date = Date.from(instant);

Note: Most likely, you would like the fraction-of-second too to be zero. If yes, just add .withNano(0) in the existing code as shown below:

OffsetDateTime.now(ZoneOffset.UTC)
    .withHour(8)
    .withMinute(45)
    .withSecond(0)
    .withNano(0)
    .toInstant();

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

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^{* 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.}