This is a infinite xp glitch using furnaces

By making a auto furnace (by putting a hopper on top of the furnace to the left and under it) and smelting items when you smelt enough items and take then out you get xp like normal. But when you take the item out of the furnace the next time you still get the same amount of xp. For example if I smelt enough items to get 30 levels and I take the item out of the furnace I get 30 levels. But when the hopper above the furnace puts another item in it and the items smelts I get the same amount of xp as before instead of it reseting when I take an item out. You can easily get hundreds of levels using this glitch.