1. Java Date Time Tutorial
2. Java System.currentTimeMillis()
3. Java Time Measurement
4. Java's java.util.Date
5. Java's java.sql.Date
6. Java's java.sql.Timestamp
7. Java's java.util.Calendar and GregorianCalendar
8. Java's java.util.TimeZone
9. Parsing and Formatting Dates in Java
10. Java Instant
11. Java Duration
12. Java LocalDate
13. Java LocalTime
14. Java LocalDateTime
15. Java ZonedDateTime
16. Java DateTimeFormatter

The static method System.currentTimeMillis() returns the time since January 1st 1970 in milliseconds. The value returned is a long. Here is an example:

long timeNow = System.currentTimeMillis();

That is really all there is to it. The returned long value can be used to initialize java.util.Date, java.sql.Date, java.sql.Timestamp and java.util.GregorianCalendar objects.

Time Granularity

The granularity of the System.currentTimeMillis() method is larger than 1 millisecond. If you call this method repeatedly, you will see that you get the same value back for a while, then it all of a sudden jumps by 10-20-30 milliseconds or more. It is not the worlds most precise or fine grained timer.