Do I have to buy Minecraft on the ps4 if I have it on xbox

Buying a game will sometimes let you play it on multiple consoles made by that company, depending on the game. As far as I know though, there has never been a case where buying it on one company's store lets you download it for free on another company's store. Buying a X-Box game will never let you play it for free on the Playstation, you have to buy it on both if you want to play it on both.