Forge Concept Registries

Registries

Registration makes a mod's objects known to the game. Registries map ResourceLocation keys to values; each registrable type has its own registry (ForgeRegistries lists Forge-wrapped ones). Names must be unique within a registry; different registries don't collide. Registering a second object with the same name overrides the first.

Methods for registering

DeferredRegister (recommended)

Maintains suppliers and registers during RegisterEvent:

private static final DeferredRegister<Block> BLOCKS = DeferredRegister.create(ForgeRegistries.BLOCKS, MODID);
public static final RegistryObject<Block> ROCK_BLOCK = BLOCKS.register("rock", () -> new Block(BlockBehaviour.Properties.of().mapColor(MapColor.STONE)));

public ExampleMod(FMLJavaModLoadingContext context) {
  // 1.21.11: use getModBusGroup() (NOT getModEventBus)
  BLOCKS.register(FMLJavaModLoadingContext.get().getModBusGroup());
}
import net.minecraftforge.fml.javafmlmod.FMLJavaModLoadingContext;

RegisterEvent

Fired for each registry after mod constructors, before config loading. Register via #register(registryKey, helper) on the mod event bus:

event.register(ForgeRegistries.Keys.BLOCKS, helper -> {
  helper.register(Identifier.fromNamespaceAndPath(MODID, "example_block_1"), new Block(...));
});

Registries that aren't Forge registries

• Static registries (e.g. LootItemConditionType): safe; use DeferredRegister.create(Registries.LOOT_CONDITION_TYPE, MODID).
• Dynamic registries (worldgen JSON registries): only registerable via data files, never in code.

Some classes register *Type factories instead (e.g. BlockEntityType, EntityType), created via their builders:

REGISTER.register("example_block_entity", () -> BlockEntityType.Builder.of(ExampleBlockEntity::new, EXAMPLE_BLOCK.get()).build(null));

Referencing registered objects

Never store registered objects in fields at registration; always reference via RegistryObject or @ObjectHolder.

• RegistryObject#create(resourceLocation, registry) → store in public static final fields, call #get().
• @ObjectHolder(registryName = "...", value = "...") on public static fields injects objects after RegisterEvent. Class-level @ObjectHolder or @Mod provides the default namespace. Missing registry/name → compile-time exception; missing object at injection → debug log, no injection.

Creating custom Forge registries

Use RegistryBuilder via NewRegistryEvent or DeferredRegister:

• NewRegistryEvent#create(builder) returns a supplier-wrapped registry (null before the event finishes).
• DeferredRegister#makeRegistry(builder) (must be called before #register on the bus).
• Datapack registries: DataPackRegistryEvent$NewRegistry#dataPackRegistry(resourceKey, codec, optionalSyncCodec) — cannot use DeferredRegister.

Missing entries

MissingMappingsEvent (fired on the Forge bus) handles removed registry objects: #getMappings(registryKey, modid) / #getAllMappings. Per Mapping, choose: IGNORE (abandon), WARN (log warning), FAIL (block world load), REMAP (remap to an existing non-null object). Default action asks the user whether to load the world.

1.21.11+ registry note

• ResourceLocation is renamed to Identifier (net.minecraft.resources.Identifier) in 1.21.11.
• Use FMLJavaModLoadingContext.get().getModBusGroup() (not getModEventBus()) to register DeferredRegisters.
• Registry lookups use lookupOrThrow, not registryOrThrow.