initFirebase.java

import com.google.firebase.*;
import com.google.firebase.iid.*;
import com.google.firebase.messaging.*;
FirebaseOptions.Builder builder = new FirebaseOptions.Builder()
                .setApplicationId("<applicationId> i.e X:XXXXXXXXXX:android:XXXXXXXXXXXXXXXXXXXXX")
                .setApiKey("<private key>")
                .setDatabaseUrl("https://yourFcmApp.firebaseio.com")
                .setStorageBucket("yourFcmApp.appspot.com");
        FirebaseApp.initializeApp(context(), builder.build());