Maezer |
Pathfinder Adventure Path, Lost Omens, Rulebook, Starfinder Adventure Path Subscriber
Spears cover a wide range of sizes. I'd be generous and say a short spear is probably interchangeable for a javelin. As both are one handed and can be thrown.
A regular spear (much less a long spear) is two handed can't be thrown and is much heavier and explicitly goes in the 3rd section.