Comment by avereveard

Anectodally[1] javac dos full builds because reading everything is faster than statting every file comparing their compiled version. Eclipse works around this keeping a change list in memory, which had its own drawback with external changes pushing the workspace out of sync

[1] I can't find a source on this but I remember having read it a long time ago, so I'll leave it at that unless I can find an actual autoritative source.