Version numbers

A version number, $VNUM, is a non-empty sequence of elements separated by period characters (U+002E). An element is either zero, or an unsigned integer numeral without leading zeros. The final element in a version number must not be zero. When an element is incremented, all subsequent elements are removed. The format is:

 [1-9][0-9]*((\.0)*\.[1-9][0-9]*)*
 

The sequence may be of arbitrary length but the first four elements are assigned specific meanings, as follows:

 $FEATURE.$INTERIM.$UPDATE.$PATCH
 

• $FEATURE — The feature-release counter, incremented for every feature release regardless of release content. Features may be added in a feature release; they may also be removed, if advance notice was given at least one feature release ahead of time. Incompatible changes may be made when justified.

• $INTERIM — The interim-release counter, incremented for non-feature releases that contain compatible bug fixes and enhancements but no incompatible changes, no feature removals, and no changes to standard APIs.

• $UPDATE — The update-release counter, incremented for compatible update releases that fix security issues, regressions, and bugs in newer features.

• $PATCH — The emergency patch-release counter, incremented only when it's necessary to produce an emergency release to fix a critical issue.

The fifth and later elements of a version number are free for use by platform implementors, to identify implementor-specific patch releases.

A version number never has trailing zero elements. If an element and all those that follow it logically have the value zero then all of them are omitted.

The sequence of numerals in a version number is compared to another such sequence in numerical, pointwise fashion; e.g., 10.0.4 is less than 10.1.2. If one sequence is shorter than another then the missing elements of the shorter sequence are considered to be less than the corresponding elements of the longer sequence; e.g., 10.0.2 is less than 10.0.2.1.

Version strings

A version string, $VSTR, is a version number $VNUM, as described above, optionally followed by pre-release and build information, in one of the following formats:

     $VNUM(-$PRE)?\+$BUILD(-$OPT)?
     $VNUM-$PRE(-$OPT)?
     $VNUM(\+-$OPT)?
 

where:

• $PRE, matching ([a-zA-Z0-9]+) — A pre-release identifier. Typically ea, for a potentially unstable early-access release under active development, or internal, for an internal developer build.

• $BUILD, matching (0|[1-9][0-9]*) — The build number, incremented for each promoted build. $BUILD is reset to 1 when any portion of $VNUM is incremented.

• $OPT, matching ([-a-zA-Z0-9.]+) — Additional build information, if desired. In the case of an internal build this will often contain the date and time of the build.

A version string 10-ea matches $VNUM = "10" and $PRE = "ea". The version string 10+-ea matches $VNUM = "10" and $OPT = "ea".

When comparing two version strings, the value of $OPT, if present, may or may not be significant depending on the chosen comparison method. The comparison methods compareTo() and compareToIgnoreOptional() should be used consistently with the corresponding methods equals() and equalsIgnoreOptional().

A short version string, $SVSTR, often useful in less formal contexts, is a version number optionally followed by a pre-release identifier:

     $VNUM(-$PRE)?
 

This is a value-based class; programmers should treat instances that are equal as interchangeable and should not use instances for synchronization, or unpredictable behavior may occur. For example, in a future release, synchronization may fail.