CommonProxy

class CommonProxy {
    public CommonProxy() {
        // Life-cycle events
        final IEventBus modEventBus = FMLJavaModLoadingContext.get().getModEventBus();
        modEventBus.addListener(CommonProxy::commonSetup);

        // Other events
        MinecraftForge.EVENT_BUS.register(this);
    }

    private static void commonSetup(FMLCommonSetupEvent event) {
        DeferredWorkQueue.runLater(() -> {
            CapabilityManager.INSTANCE.register(IModTag.class, new ModTagStorage(), ModTagProvider::new);
        });
    }

    static class ClientProxy extends CommonProxy {
        ClientProxy() {
            final IEventBus modEventBus = FMLJavaModLoadingContext.get().getModEventBus();
            modEventBus.addListener(ClientProxy::clientSetup);
            modEventBus.addListener(ModEvents::registerItemColor);
        }

        private static void clientSetup(FMLClientSetupEvent event) { }
    }

    static class ServerProxy extends CommonProxy {
        ServerProxy() {
            final IEventBus modEventBus = FMLJavaModLoadingContext.get().getModEventBus();
            modEventBus.addListener(ServerProxy::serverSetup);
        }

        private static void serverSetup(FMLDedicatedServerSetupEvent event) { }
    }
}