this is my code

@SubscribeEvent
    public void checkItem(BlockEvent.EntityPlaceEvent event) {
        if (!event.getWorld().isRemote()) {
            if (event.getEntity() instanceof PlayerEntity) {
                PlayerEntity player = (PlayerEntity) event.getEntity();
                Hand hand = player.getActiveHand();
                ItemStack stack = player.getHeldItem(hand);
                System.out.println(stack);
                if (stack.getCount() == 1) {
                    System.out.println(stack);
                    int i = this.findItem(player, stack.getItem().getItem());
                    if (i != -1) {
                        ItemStack item = player.inventory.mainInventory.get(i);
                        player.inventory.mainInventory.set(i, ItemStack.EMPTY);
                        player.setHeldItem(hand, item);
                        System.out.println(stack + " 1");
                    }
                }
            }
        }
    }

public int findItem(PlayerEntity player, Item item) {
        for (int i = 0; i < player.inventory.getSizeInventory(); i++) {
            ItemStack stack = player.inventory.mainInventory.get(i);
            if (!stack.isEmpty() && stack.getItem().getItem() == item) {
                return i;
            }
        }
        return -1;
    }

 

Edited August 17, 20214 yr by IamP
syntax highlighting

Thanks for your recommendation

It's work now.