The Main Mod Class and the Event Bus

Every Forge mod has one main class, annotated with @Mod, that Forge instantiates automatically when the game loads.

package com.example.examplemod;

import net.minecraftforge.fml.common.Mod;
import net.minecraftforge.fml.javafmlmod.FMLJavaModLoadingContext;

@Mod("examplemod")
public class ExampleMod {
    public ExampleMod() {
        FMLJavaModLoadingContext.get().getModEventBus()
            .addListener(this::commonSetup);
    }

    private void commonSetup(final FMLCommonSetupEvent event) {
        // runs once, early, on both client and dedicated server
    }
}

The string passed to @Mod must match modId in mods.toml, that's how Forge connects the class to the mod's metadata.

The mod event bus

Forge fires setup and registration events through a mod event bus, retrieved with FMLJavaModLoadingContext.get().getModEventBus(). Registering a listener in the constructor, as above, is the standard place to hook into it, you'll register items and blocks here in the next two lessons.

FMLCommonSetupEvent fires once, after all registries have finished registering, the right place for setup logic that depends on other mods' content already existing (like inter-mod compatibility), but too early for anything requiring a running world.