@EventHandler
public void onPlayerItemConsume(PlayerItemConsumeEvent event) {
	if(event.getItem().getType().equals(Material.POISONOUS_POTATO)) {
		event.setCancelled(true);
		ItemStack item = event.getPlayer().getInventory().getItemInHand();
		
		if(item.getAmount() <= 1) {
			event.getPlayer().getInventory().setItemInHand(new ItemStack(Material.AIR));
		} else {
			item.setAmount(item.getAmount() - 1);
			event.getPlayer().getInventory().setItemInHand(item);
		}
		@SuppressWarnings("deprecation")
		event.getPlayer().updateInventory();

		//Dein restlicher Code\\

	}
}