Drain the pineapple, reserving 3 tablespoons juice. Arrange pineapple on the bottom of a greased 1.5 casserole dish. Stir together the flour and sugar and sprinkle over the pineapple. Drizzle the reserved pineapple liquid over the contents in the dish. Top with the cheddar cheese. Mix together the crushed crackers and the melted butter and distribute over the cheese. Bake the casserole, covered, in a 350 degree oven for 15 minutes. Uncover and bake 10 minutes longer