how to solve java.lang.NullPointerException: invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference

Question

when I run my app on Mobile device after open profile Activity for fetch data from firebase data base then my app is crashed. after see debug in android studio I have see this issue

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference at .MainActivity$1.onDataChange(MainActivity.java:83)

here is Line 83:

 String imageUrl = snapshot.child("profilepictureurl").getValue().toString();

here is the whole of MainActivity.java

import android.content.Intent;
import android.os.Bundle;
import android.view.MenuItem;
import android.widget.ImageView;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.appcompat.app.ActionBarDrawerToggle;
import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;
import androidx.core.view.GravityCompat;
import androidx.drawerlayout.widget.DrawerLayout;

import com.bumptech.glide.Glide;
import com.google.android.material.navigation.NavigationView;
import com.google.firebase.auth.FirebaseAuth;
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;

public class MainActivity extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener {

    private DrawerLayout drawerLayout;
    private Toolbar toolbar;
    private NavigationView nav_view;
    private ImageView nav_profile_image;
    private TextView nav_fullname, nav_user_phone ,nav_user_email, nav_user_bloodgroup, nav_user_type;
    private DatabaseReference userRef;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        getSupportActionBar().setTitle("SYP Blood Bank");

        drawerLayout = findViewById(R.id.drawerLayout);
        nav_view = findViewById(R.id.nav_view);

        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(MainActivity.this, drawerLayout, toolbar,
                R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawerLayout.addDrawerListener(toggle);
        toggle.syncState();

        nav_view.setNavigationItemSelectedListener(this);

        nav_profile_image = nav_view.getHeaderView(0).findViewById(R.id.nav_user_image);
        nav_fullname = nav_view.getHeaderView(0).findViewById(R.id.nav_fullname);
        nav_user_email = nav_view.getHeaderView(0).findViewById(R.id.nav_user_email);
        nav_user_bloodgroup = nav_view.getHeaderView(0).findViewById(R.id.nav_user_bloodgroup);
        nav_user_type = nav_view.getHeaderView(0).findViewById(R.id.nav_user_type);
        nav_user_phone = nav_view.getHeaderView(0).findViewById(R.id.nav_user_phone);

        userRef = FirebaseDatabase.getInstance().getReference().child("users").child(FirebaseAuth.getInstance().getCurrentUser()
                .getUid());

        userRef.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {

                if (snapshot.exists()){
                    String name = snapshot.child("name").getValue().toString();
                    nav_fullname.setText(name);

                    String email = snapshot.child("email").getValue().toString();
                    nav_user_email.setText(email);

                    String phonenumber = snapshot.child("phonenumber").getValue().toString();
                    nav_user_phone.setText(phonenumber);

                    String bloodgroup = snapshot.child("bloodgroup").getValue().toString();
                    nav_user_bloodgroup.setText(bloodgroup);

                    String type = snapshot.child("type").getValue().toString();
                    nav_user_type.setText(type);

                    String imageUrl = snapshot.child("profilepictureurl").getValue().toString();
                    Glide.with(getApplicationContext()).load(imageUrl).into(nav_profile_image);

                }
            }

            @Override
            public void onCancelled(@NonNull DatabaseError error) {

            }
        });

    }

    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem item) {
        switch (item.getItemId()){
            case R.id.profile:
                Intent intent = new Intent(MainActivity.this, ProfileActivity.class);
                startActivity(intent);
        }
        drawerLayout.closeDrawer(GravityCompat.START);
        return true;
    }
}

Answer 1

NullPointerException means that the value of your imageUrl is null (has no value), make sur that the name of your firebase node (child) is named in your code same as in your RealtimeDatabase then check its value :

if(imageUrl != null) {
//do your stuff
}