Flutter Project: MainActivity.java is missing

flutter create -a java .

Try this command. with '.' at end. It represent current project directory. apply this command from project root folder. This command will try to recreate android project with java (this will setup your MainActiviy.java). It won't affect currently setup manifest or any other firebase related setup.

If you are here because you are following the steps for setting up firebase_messaging, you can look at this answer and just create the Application.kt file (instead of Java) next to your MainActivity.kt file. Here it is:

package com.example.yourapp

import io.flutter.app.FlutterApplication
import io.flutter.plugin.common.PluginRegistry
import io.flutter.plugin.common.PluginRegistry.PluginRegistrantCallback
import io.flutter.plugins.GeneratedPluginRegistrant
import io.flutter.plugins.firebasemessaging.FlutterFirebaseMessagingService

class Application : FlutterApplication(), PluginRegistrantCallback {

    override fun onCreate() {
        super.onCreate()
        FlutterFirebaseMessagingService.setPluginRegistrant(this);
    }

    override fun registerWith(registry: PluginRegistry?) {
        io.flutter.plugins.firebasemessaging.FirebaseMessagingPlugin.registerWith(registry?.registrarFor("io.flutter.plugins.firebasemessaging.FirebaseMessagingPlugin"));
    }
}

You can simply create the class file MainActivity.java with the Java code and delete the Kotlin one. It should work:

public class MainActivity extends FlutterActivity {

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    GeneratedPluginRegistrant.registerWith(this);
  }
}