public class BoxBlockEntity extends BlockEntity implements NamedScreenHandlerFactory, ImplementedInventory {
    private final DefaultedList<ItemStack> inventory = DefaultedList.ofSize(9, ItemStack.EMPTY);

    public BoxBlockEntity(BlockPos pos, BlockState state) {
        super(ExampleMod.BOX_BLOCK_ENTITY, pos, state);
    }


    // From the ImplementedInventory Interface

    @Override
    public DefaultedList<ItemStack> getItems() {
        return inventory;
    }

    // These Methods are from the NamedScreenHandlerFactory Interface
    // createMenu creates the ScreenHandler itself
    // `getDisplayName` will Provide its name which is normally shown at the top

    @Override
    public ScreenHandler createMenu(int syncId, PlayerInventory playerInventory, PlayerEntity player) {
        // We provide *this* to the screenHandler as our class Implements Inventory
        // Only the Server has the Inventory at the start, this will be synced to the client in the ScreenHandler
        return new BoxScreenHandler(syncId, playerInventory, this);
    }

    @Override
    public Text getDisplayName() {
        // for 1.19+
        return Text.translatable(getCachedState().getBlock().getTranslationKey());
        // for earlier versions
        // return new TranslatableText(getCachedState().getBlock().getTranslationKey());
    }
    
    // For the following two methods, for earlier versions, remove the parameter `registryLookup`.
    @Override
    public void readNbt(NbtCompound nbt, RegistryWrapper.WrapperLookup registryLookup) {
        super.readNbt(nbt, registryLookup);
        Inventories.readNbt(nbt, this.inventory, registryLookup);
    }

    @Override
    public NbtCompound writeNbt(NbtCompound nbt, RegistryWrapper.WrapperLookup registryLookup) {
        super.writeNbt(nbt, registryLookup);
        Inventories.writeNbt(nbt, this.inventory, registryLookup);
        return nbt;
    }
}