Before you can use Realm in your application, you must initialize it. This only has to be done once using method Realm.init(context); You must provide an Android context. A good place to initialize Realm is in onCreate method of an application subclass. If you create your own application subclass, you must add it to the AndroidManifest.xml

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AndroidManifest.xml

    ...
    
    ...

MyApplication.java

public class MyApplication extends Application {

 @Override
 public void onCreate() {
  super.onCreate();
  Realm.init(this); // Initialize Realm
 }

}

MyActivity.java

public class MyActivity extends Activity {

 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  Realm realm = Realm.getDefaultInstance(); // Get a Realm instance for this thread
  try {
   // ... Do something ...
  } finally {
   realm.close();
  }
 }

}