Solved Adding items to a hopper.

Hi, I'm making a plugin to save the enchantments of the weapons in an enchanted book after disenchanting them in the grindstone, for that I'm using a hopper.
(I'm making this thread because I did not find any solution related to my problem in the forums)

The problems start when I want to add this book (after creating it) inside a hopper. I can store it (the book) inside a chest, but not inside a hopper.

I decided to go step by step, and try to add a diamond inside a hopper, using the BlockPlaceEvent event.

Code (Java):

package me.matsuneitor.grindstoneenchanter.Events;

import org.bukkit.ChatColor;
import org.bukkit.Material;
import org.bukkit.block.Hopper;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.block.BlockPlaceEvent;
import org.bukkit.inventory.ItemStack;

public class BlockPlace implements Listener {

    @EventHandler
    public void onBlocKPlace(BlockPlaceEvent event) {
        if(event.getBlockPlaced().getType().equals(Material.HOPPER)) {
            event.getPlayer().sendMessage(ChatColor.AQUA + "¡Diamonds!");
            Hopper hopper = (Hopper) event.getBlockPlaced().getState();
            ItemStack itemStack = new ItemStack(Material.DIAMOND);
            hopper.getInventory().addItem(itemStack);
            hopper.update();
        }
    }
}

I've already registered the event, when I place a hopper somewhere, I receive the message "Diamonds!" but the hopper's still empty.

¿What am I doing wrong?

I'm using 1.15.2.

 

I couldn't find that method.

I just tried it, but it still doesn't work.

Thanks to both anyway.

 

yup, that's for chests.

I found the solution, changed from getInventory() to getSnapshotInventory() and now it works. Thanks y'all for the help.