the build number is dynamically set at build time. if a build number is not specified, it doesn't show in the about box. to specify a build number, when building with ant use:
ant <your_target> -Dbuild.number=<your_build_number>
bamboo does something similar to:
ant clean jar -Dbuild.number=${bamboo.buildNumber}
you can specify your own build number by doing something like:
ant clean release -Dbuild.number=9000
passing the build number into ant was the only way to get dynamic build numbers. it's also generic enough that people doing their own builds can specify custom build numbers easily. note that spark's version (ie. 2.7.0) is also set dynamically at build time from the version specified inside the ant build script. both being set at build time has the added benefit that nobody has to remember to bump all the version numbers! 