Comparison of the Instant and Date Classes

By | 2014-08-12

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Java 8 has a new java.time package, and one of its new classes is Instant. The best counterpart to this in past platforms is the java.util.Date class.

There are a couple notable differences between Date and Instant:

  • Date has very few useful methods, and Instant provides many.
  • Instant provides finer time granularity and a longer timeline.

Most of Date’s methods have been deprecated. Date manipulation and formatting have been delegated to the Calendar and DateFormat classes. In comparison, the Instant class allows you to perform some very basic functionality directly. You can add seconds and milliseconds for example. You can parse and generate ISO 8601 date strings with Instant as well. ISO 8601 dates have a consistent form across all locales and look like this: 2014-08-12T14:51:53:00Z. Most of the Instant methods are purely for convenience. You can do the similar things with Date using the Calendar and DateFormat classes.

Both Date and Instant have the same epoch (1970-01-01T00:00:00Z), but Instant can represent a much longer timeline. Date’s internal structure uses a long to represent milliseconds from the epoch. Instant, however, uses a long to represent seconds from epoch AND an int to represent nanoseconds of that second. That certainly means you don’t have to worry about date rollover problems in the near future.

The differences between Date and Instant are relatively minor, but these classes really are the starting point of of a more thorough discussion of the java.time package. Expect more details in the near future.

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