public class DemoBlock extends BlockWithEntity {
 
    [...]
 
    @Override
    public void appendTooltip(ItemStack stack, BlockView world, List<Text> tooltip, TooltipContext context) {
        NbtCompound nbt = BlockItem.getBlockEntityNbt(stack);
        if (nbt == null) return;

        tooltip.add(Text.literal("数字： " + nbt.getInt("number"))
    }
}