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Jankeyfu
Jankeyfu

Reputation: 29

something about the result of Date(long date )

The JDK1.8 API saies the result of the Date(long date) is based on the time January 1, 1970, 00:00:00 GMT, but when I test it by set the date=0, I find the result is not the Thu Jan 01 08:00:00 CST 1970, it's not the 00:00:00,but the 08:00:00,why?the result about the Date(long date)

Upvotes: 1

Views: 77

Answers (3)

Basil Bourque
Basil Bourque

Reputation: 339043

tl;dr

Instant.EPOCH.toString()

1970-01-01T00:00:00Z

Instant.EPOCH.atZone( ZoneId.of( "America/Chicago" ) ).toString()  // Use proper time zone names (continent/region). Avoid pseudo-zones such as `CST`, which could be Central Standard Time in US or China Standard Time.

1969-12-31T18:00-06:00[America/Chicago]

Instant.EPOCH.atZone( ZoneId.of( "Asia/Hong_Kong" ) ).toString()

1970-01-01T08:00+08:00[Asia/Hong_Kong]

Avoid legacy date-time classes

You are using you using old date-time classes, now legacy, supplanted by the java.time classes.

Among its many problems, the toString method of java.util.Date implicitly applies the JVM’s current default time zone while generating a string. Avoid this class.

java.time

Instead use Instant. Represents a moment on the timeline in UTC with a resolution of nanoseconds.

Instant.ofEpochSecond( 0 ).toString()

1970-01-01T00:00:00Z

Or use the constant for that value, Instant.EPOCH.

For current moment in UTC, call now.

Instant.now()

To adjust into a specific time zone, search Stack Overflow for ZonedDateTime and ZoneId.

Adjust into another time zone. Same moment, same simultaneous point on the time line, but different wall-clock time.

Specify a proper time zone name in the format of continent/region, such as America/Montreal, Africa/Casablanca, or Pacific/Auckland. Never use the 3-4 letter abbreviation such as EST or IST as they are not true time zones, not standardized, and not even unique(!). 

ZoneId z = ZoneId.of( "Asia/Hong_Kong" ) ;
ZonedDateTime zdt = instant.atZone( z ) ;

About java.time

The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date, Calendar, & SimpleDateFormat.

The Joda-Time project, now in maintenance mode, advises migration to the java.time classes.

To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations. Specification is JSR 310.

With a JDBC driver complying with JDBC 4.2 or later, you may exchange java.time objects directly with your database. No need for strings or java.sql.* classes.

Where to obtain the java.time classes?

The ThreeTen-Extra project extends java.time with additional classes. This project is a proving ground for possible future additions to java.time. You may find some useful classes here such as Interval, YearWeek, YearQuarter, and more.

Upvotes: 0

Vasu
Vasu

Reputation: 22442

It is because of the TimeZone set, by default by the JVM when & where you run the program, look at the below statement from the Java doc.

Typically, you get a TimeZone using getDefault which creates a TimeZone based on the time zone where the program is running. For example, for a program running in Japan, getDefault creates a TimeZone object based on Japanese Standard Time.

You can look at here

Upvotes: 0

Ashraful Islam
Ashraful Islam

Reputation: 12840

It's because of your timezone. If you change the time zone to GMT it will show 00:00:00

Date date = new Date(0L);
TimeZone.setDefault(TimeZone.getTimeZone("GMT"));
System.out.println(date);

Output : Thu Jan 01 00:00:00 GMT 1970

Upvotes: 1

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