public class ExampleMod implements ModInitializer {

    public static final Block BOX_BLOCK;
    public static final BlockItem BOX_BLOCK_ITEM;
    public static final BlockEntityType<BoxBlockEntity> BOX_BLOCK_ENTITY;

    public static final String MOD_ID = "testmod";
    // a public identifier for multiple parts of our bigger chest
    public static final Identifier BOX = new Identifier(MOD_ID, "box_block");

    static {
        BOX_BLOCK = Registry.register(Registries.BLOCK, BOX, new BoxBlock(FabricBlockSettings.copyOf(Blocks.CHEST)));
        BOX_BLOCK_ITEM = Registry.register(Registries.ITEM, BOX, new BlockItem(BOX_BLOCK, new Item.Settings()));

        //The parameter of build at the very end is always null, do not worry about it
        // pre-1.17
        BOX_BLOCK_ENTITY = Registry.register(Registry.BLOCK_ENTITY_TYPE, BOX, BlockEntityType.Builder.create(BoxBlockEntity::new, BOX_BLOCK).build(null));
        // In 1.17 use FabricBlockEntityTypeBuilder instead of BlockEntityType.Builder
        BOX_BLOCK_ENTITY = Registry.register(Registry.BLOCK_ENTITY_TYPE, BOX, FabricBlockEntityTypeBuilder.create(BoxBlockEntity::new, BOX_BLOCK).build(null));
    }

    @Override
    public void onInitialize() {

    }
}