Fabric classload register

Mod.java

public class Mod implements ModInitializer {
    public static final String MODID = "mod";
  
    @Override
    public void onInitialize() {
        ModItems.initItems();
    }
}

ModItems.java

public class ModItems {
    public static void initItems() {}
  
    public static Item ITEM_A = RegisterItem("item_a", (key) -> new Item(new Item.Properties().setId(key)));
    public static Item ITEM_B = RegisterItem("item_b", (key) -> new Item(new Item.Properties().setId(key)));

    private static Item RegisterItem(String itemName, Function<ResourceKey<Item>, Item> itemSupplier) {
        ResourceKey<Item> itemResourceKey = ResourceKey.create(Registries.ITEM, ResourceLocation.fromNamespaceAndPath(MODID, itemName));
        return Registry.register(Registries.ITEM, itemResourceKey.location(), itemSupplier.apply(itemResourceKey));
    }
}