Non-deferred NeoForge

Mod.java

@Mod(Mod.MODID)
public class Mod {
    public static final String MODID = "mod";
  
    public Mod(IEventBus modEventBus, ModContainer modContainer) {
        modEventBus.addListener(ModItems::ModRegisterEvent);
    }
}

ModItems.java

public class ModItems {
    public static Item ITEM_A;
    public static Item ITEM_B;
  
    private static void ModRegisterEvent(RegisterEvent registerEvent) {
        ITEM_A = RegisterItem(registerEvent, "item_a", (key) -> new Item(new Item.Properties().setId(key)));
        ITEM_B = RegisterItem(registerEvent, "item_b", (key) -> new Item(new Item.Properties().setId(key)));
    }
    
    private static void RegisterItem(RegisterEvent registerEvent, String itemName, Function<ResourceKey<Item>, Item> itemSupplier) {
        ResourceKey<Item> itemResourceKey = ResourceKey.create(Registries.ITEM, ResourceLocation.fromNamespaceAndPath(MODID, itemName));
        registerEvent.register(Registries.ITEM, itemResourceKey.location(), () -> itemSupplier.apply(itemResourceKey));
    }
}