Firebase数据库Android Studio

buildscript {
    dependencies {
        classpath 'com.google.gms:google-services:4.3.10'
    }
}

apply plugin: 'com.android.application'
apply plugin: 'com.google.gms.google-services'

dependencies {
    implementation 'com.google.firebase:firebase-database:20.0.3'
}

import com.google.firebase.FirebaseApp;

public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // Initialize Firebase
        FirebaseApp.initializeApp(this);
    }
}

import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;

// ...

FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference myRef = database.getReference("message");

myRef.setValue("Hello, World!");

import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.ValueEventListener;

// ...

myRef.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        // This method is called once with the initial value and again
        // whenever data at this location is updated.
        String value = dataSnapshot.getValue(String.class);
        Log.d(TAG, "Value is: " + value);
    }

    @Override
    public void onCancelled(DatabaseError error) {
        // Failed to read value
        Log.w(TAG, "Failed to read value.", error.toException());
    }
});