public class SlotBackpack extends Slot {

    SlotBackpack(IInventory iinventory, int i, int j, int k) {
        super(iinventory, i, j, k);
    }

    public int getSlotStackLimit() {
        return 64;
    }

    public boolean isItemValid(ItemStack itemstack) {
        return itemstack != null && !(itemstack.getItem() instanceof ItemBackpack);
    }

}