Multiple Firebase projects in a single android application

I'm trying to build an android application using Firebase that demands two separate databases (teachers and students) in a single application. I searched for the solution all over the internet but all I got is this solution- Multiple Firebase projects in one app, which seems to be a great solution but I didn't understand.

So, how do I merge two firebase projects in a single application?

Yes, you can follow that guide https://firebase.google.com/docs/projects/multiprojects#java.

Basically, you need to initiate the firebase app providing configuration manually

        // [START firebase_options]
    // Manually configure Firebase Options. The following fields are REQUIRED:
    //   - Project ID
    //   - App ID
    //   - API Key
    FirebaseOptions options1 = new FirebaseOptions.Builder()
            .setProjectId("my-firebase-project")
            .setApplicationId("1:27992087142:android:ce3b6448250083d1")
            .setApiKey("AIzaSyADUe90ULnQDuGShD9W23RDP0xmeDc6Mvw")
            // setDatabaseURL(...)
            // setStorageBucket(...)
            .build();
    FirebaseOptions options2 = new FirebaseOptions.Builder()
            .setProjectId("my-firebase-project")
            .setApplicationId("1:27992087142:android:ce3b6448250083d1")
            .setApiKey("AIzaSyADUe90ULnQDuGShD9W23RDP0xmeDc6Mvw")
            // setDatabaseURL(...)
            // setStorageBucket(...)
            .build();
    // [END firebase_options]


    // [START firebase_secondary]
    // Initialize with secondary app
    FirebaseApp.initializeApp(this /* Context */, options1, "first");
    FirebaseApp.initializeApp(this /* Context */, options2, "secondary");


    FirebaseApp first = FirebaseApp.getInstance("first");
    FirebaseApp secondary = FirebaseApp.getInstance("secondary");

You can get all required data from google-service.json

Later you can get a database from that FirebaseApp, for example

FirebaseDatabase secondaryDatabase = FirebaseDatabase.getInstance(secondary);

Then you just work with the project like before.