May I ask what is the application of a spear?

In pre-modern times some samurai households did keep spears for the purposes of defense, but they were typically mounted in such a way that people could take them out of the house easily (i.e., near the main entrance, requiring awkwardly manoeuvering around corners). Long weapons like spears are for outdoor use. Indoor fighting requires short weapons. There are shorter "hand spears," but still they are intended for outdoor use. But if you're talking about a three-foot stick with a spike at the end, it seems more likely.