sample project

src/main/java/net/fabricmc/example/ExampleMod.java

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+package net.fabricmc.example;
+
+import net.fabricmc.api.ModInitializer;
+
+public class ExampleMod implements ModInitializer {
+	@Override
+	public void onInitialize() {
+		// This code runs as soon as Minecraft is in a mod-load-ready state.
+		// However, some things (like resources) may still be uninitialized.
+		// Proceed with mild caution.
+
+		System.out.println("Hello Fabric world!");
+	}
+}

src/main/java/net/fabricmc/example/mixin/ExampleMixin.java

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+package net.fabricmc.example.mixin;
+
+import net.minecraft.client.gui.screen.TitleScreen;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
+
+@Mixin(TitleScreen.class)
+public class ExampleMixin {
+	@Inject(at = @At("HEAD"), method = "init()V")
+	private void init(CallbackInfo info) {
+		System.out.println("This line is printed by an example mod mixin!");
+	}
+}