Why timestamp of different days are same without part of time?

user_7832012 0
Viewed 127
    public static void main(String[] args) throws ParseException {
        long DAY = 1000 * 60 * 60 * 24;

        SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        Date yDate = simpleDateFormat.parse("2020-06-12 23:58:33");
        System.out.println(yDate.getTime() - (yDate.getTime() % DAY));

        Date date = simpleDateFormat.parse("2020-06-13 00:29:38");
        System.out.println(date.getTime() - date.getTime() % DAY);
    }

the console print: 1591920000000 1591920000000

timestamp java
2 Answers

Here's an example of solving your problem with java.time instead of the outdated classes from java.util:

public static void main(String[] args) {
    // define an up-to-date(-time) formatter and specify the output language
    DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss",
                                                    Locale.ENGLISH);
    // define two timezones to be used later
    ZoneId shanghai = ZoneId.of("Asia/Shanghai");
    ZoneId utc = ZoneId.of("UTC");

    /*
     * Parse the datetimes to a ZonedDateTime each, because timezones matter here...
     * This uses two different ones in order to highlight how timezones matter here
     */
    ZonedDateTime zdtShanghaiOne = LocalDateTime.parse("2020-06-12 23:58:33", dtf)
                                                    .atZone(shanghai);
    ZonedDateTime zdtShanghaiTwo = LocalDateTime.parse("2020-06-13 00:29:38", dtf)
                                                    .atZone(shanghai);
    ZonedDateTime zdtUtcOne = LocalDateTime.parse("2020-06-12 23:58:33", dtf)
                                                    .atZone(utc);
    ZonedDateTime zdtUtcTwo = LocalDateTime.parse("2020-06-13 00:29:38", dtf)
                                                    .atZone(utc);
    /*
     * Print the millis as a result of subtracting the time information.
     * Acutally, this way to get a datetime of the form "yyyy-MM-dd'T'00:00:00.0'Zone'"
     * takes the datetime and returns the same date with a time of 0 hours, minutes, seconds...
     */
    System.out.println("Shanghai millis day one:\t"
                + zdtShanghaiOne.with(LocalTime.MIN).toInstant().toEpochMilli());
    System.out.println("Shanghai millis day two:\t"
                + zdtShanghaiTwo.with(LocalTime.MIN).toInstant().toEpochMilli());
    System.out.println("UTC millis day one:\t\t"
                + zdtUtcOne.with(LocalTime.MIN).toInstant().toEpochMilli());
    System.out.println("UTC millis day two:\t\t"
                + zdtUtcTwo.with(LocalTime.MIN).toInstant().toEpochMilli());
}

This leads to an output of

Shanghai millis day one:    1591891200000
Shanghai millis day two:    1591977600000
UTC millis day one:         1591920000000
UTC millis day two:         1592006400000

It's really recommended to use java.time to not have to rely on own calculations that may fail because of missing timezone information (to code and / or coder).

user_17121350

It is because of time zone. Those dates are not on a DAY boundary because of time zone, try

        SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss Z");
        Date yDate = simpleDateFormat.parse("2020-06-12 23:58:33 +0000");
        System.out.println(yDate.getTime() - (yDate.getTime() % DAY));

        Date date = simpleDateFormat.parse("2020-06-13 00:29:38 +0000");
        System.out.println(date.getTime() - (date.getTime() % DAY));
user_75154920
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