Android studio - Java Null-pointer on Firebase invocation

The actual error I receive when running the program is:

java.lang.NullPointerException: Attempt to invoke virtual method 'com.google.firebase.database.DatabaseReference com.google.firebase.database.DatabaseReference.child(java.lang.String)' on a null object reference

This is my firebase database class:

    import android.location.Location;  import android.util.Log;    import androidx.annotation.NonNull;    import com.google.firebase.database.DataSnapshot;  import com.google.firebase.database.DatabaseError;  import com.google.firebase.database.DatabaseReference;  import com.google.firebase.database.FirebaseDatabase;  import com.google.firebase.database.ValueEventListener;    import java.util.ArrayList;  import java.util.List;    public class FirebaseDatabaseHelper {      public static FirebaseDatabase mDatabase ;      public static DatabaseReference mReferenceCrossings;     // public static DataSnapshot dataSnapshot;        public FirebaseDatabaseHelper(FirebaseDatabase mDatabase) {         mDatabase = FirebaseDatabase.getInstance();          mReferenceCrossings = mDatabase.getReference();      }              public static ArrayList<Location> sortedQuery(String reference, String orderKey) {          ArrayList<Location> results = new ArrayList<Location>();          DatabaseReference targetRef = mReferenceCrossings.child(reference);          targetRef.orderByChild(orderKey).addListenerForSingleValueEvent(new ValueEventListener() {              @Override              public void onDataChange(@NonNull DataSnapshot datasnapshot) {                  for (DataSnapshot child : datasnapshot.getChildren()) {                      double latitude = Double.parseDouble(child.child("Latitude").getValue().toString());                      double longitude = Double.parseDouble(child.child("Longitude").getValue().toString());                      Location entry = new Location("coordinates");                      entry.setLatitude(latitude);                      entry.setLongitude(longitude);                      results.add(entry);                      Log.d("coordinates", results.toString());                  }              }                @Override              public void onCancelled(@NonNull DatabaseError error) {                  Log.d("Firebase error", error.getDetails());              }          });          return results;        }            }    

This is my main class:

package com.example.locationpushing;    import androidx.annotation.NonNull;  import androidx.annotation.Nullable;  import androidx.core.app.ActivityCompat;  import androidx.core.content.ContextCompat;  import androidx.fragment.app.FragmentActivity;    import android.Manifest;  import android.content.Intent;  import android.content.IntentSender;  import android.content.pm.PackageManager;  import android.graphics.Color;  import android.location.Address;  import android.location.Geocoder;  import android.location.Location;  import android.os.Bundle;  import android.os.Looper;  import android.util.Log;    import com.google.android.gms.common.api.ResolvableApiException;  import com.google.android.gms.location.FusedLocationProviderClient;  import com.google.android.gms.location.LocationCallback;  import com.google.android.gms.location.LocationRequest;  import com.google.android.gms.location.LocationResult;  import com.google.android.gms.location.LocationServices;  import com.google.android.gms.location.LocationSettingsRequest;  import com.google.android.gms.location.LocationSettingsResponse;  import com.google.android.gms.location.SettingsClient;  import com.google.android.gms.maps.CameraUpdate;  import com.google.android.gms.maps.CameraUpdateFactory;  import com.google.android.gms.maps.GoogleMap;  import com.google.android.gms.maps.LocationSource;  import com.google.android.gms.maps.OnMapReadyCallback;  import com.google.android.gms.maps.SupportMapFragment;  import com.google.android.gms.maps.model.BitmapDescriptorFactory;  import com.google.android.gms.maps.model.Circle;  import com.google.android.gms.maps.model.CircleOptions;  import com.google.android.gms.maps.model.LatLng;  import com.google.android.gms.maps.model.Marker;  import com.google.android.gms.maps.model.MarkerOptions;  import com.google.android.gms.tasks.OnCompleteListener;  import com.google.android.gms.tasks.OnFailureListener;  import com.google.android.gms.tasks.OnSuccessListener;  import com.google.android.gms.tasks.Task;    import androidx.annotation.NonNull;  import androidx.core.app.ActivityCompat;  import androidx.core.content.ContextCompat;  import androidx.fragment.app.FragmentActivity;    import android.Manifest;  import android.content.pm.PackageManager;  import android.location.Address;  import android.location.Geocoder;  import android.location.Location;  import android.os.Bundle;  import android.util.Log;    import com.google.android.gms.location.FusedLocationProviderClient;  import com.google.android.gms.location.LocationServices;  import com.google.android.gms.maps.CameraUpdateFactory;  import com.google.android.gms.maps.GoogleMap;  import com.google.android.gms.maps.OnMapReadyCallback;  import com.google.android.gms.maps.SupportMapFragment;  import com.google.android.gms.maps.model.LatLng;  import com.google.android.gms.maps.model.MarkerOptions;  import com.google.android.gms.tasks.OnSuccessListener;  import com.google.android.gms.tasks.Task;  import com.google.firebase.database.FirebaseDatabase;  import com.google.firebase.messaging.FirebaseMessaging;  import com.google.firebase.messaging.RemoteMessage;    import java.io.IOException;  import java.util.Collection;  import java.util.List;  import java.util.Map;  import java.util.Set;    public class MapsActivity extends FragmentActivity implements OnMapReadyCallback {        private static final String TAG = "MapsActivity";      private GoogleMap mMap;      private Geocoder geocoder;      private int ACCESS_LOCATION_REQUEST_CODE = 10001;      FusedLocationProviderClient fusedLocationProviderClient;      LocationRequest locationRequest;        Marker userLocationMarker;      Circle userLocationAccuracyCircle;          @Override      protected void onCreate(Bundle savedInstanceState) {          super.onCreate(savedInstanceState);          setContentView(R.layout.activity_maps);          // Obtain the SupportMapFragment and get notified when the map is ready to be used.          SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()                  .findFragmentById(R.id.map);          mapFragment.getMapAsync(this);          geocoder = new Geocoder(this);          fusedLocationProviderClient = LocationServices.getFusedLocationProviderClient(this);          locationRequest = LocationRequest.create();          locationRequest.setInterval(330);          locationRequest.setFastestInterval(330);          locationRequest.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY);            Intent intentBackgroundService = new Intent(this, FirebasePushNotification.class);          startService(intentBackgroundService);         FirebaseDatabaseHelper.sortedQuery("mReferenceCrossings","Latitude");  }  

I've attempted different solutions but I still receive nullPointerException for the database. How could I properly initialize the database for access?

I would really appreciate the help on this. Thank you for any advice given.

https://stackoverflow.com/questions/66631184/android-studio-java-null-pointer-on-firebase-invocation March 15, 2021 at 09:10AM