protected void onCreate()

in messaging/app/src/main/java/com/google/firebase/quickstart/fcm/java/MainActivity.java [41:120]
56 lines of code
6 McCabe index (conditional complexity)

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        ActivityMainBinding binding = ActivityMainBinding.inflate(getLayoutInflater());
        setContentView(binding.getRoot());

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            // Create channel to show notifications.
            String channelId  = getString(R.string.default_notification_channel_id);
            String channelName = getString(R.string.default_notification_channel_name);
            NotificationManager notificationManager =
                    getSystemService(NotificationManager.class);
            notificationManager.createNotificationChannel(new NotificationChannel(channelId,
                    channelName, NotificationManager.IMPORTANCE_LOW));
        }

        // If a notification message is tapped, any data accompanying the notification
        // message is available in the intent extras. In this sample the launcher
        // intent is fired when the notification is tapped, so any accompanying data would
        // be handled here. If you want a different intent fired, set the click_action
        // field of the notification message to the desired intent. The launcher intent
        // is used when no click_action is specified.
        //
        // Handle possible data accompanying notification message.
        // [START handle_data_extras]
        if (getIntent().getExtras() != null) {
            for (String key : getIntent().getExtras().keySet()) {
                Object value = getIntent().getExtras().get(key);
                Log.d(TAG, "Key: " + key + " Value: " + value);
            }
        }
        // [END handle_data_extras]

        binding.subscribeButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Log.d(TAG, "Subscribing to weather topic");
                // [START subscribe_topics]
                FirebaseMessaging.getInstance().subscribeToTopic("weather")
                        .addOnCompleteListener(new OnCompleteListener<Void>() {
                            @Override
                            public void onComplete(@NonNull Task<Void> task) {
                                String msg = getString(R.string.msg_subscribed);
                                if (!task.isSuccessful()) {
                                    msg = getString(R.string.msg_subscribe_failed);
                                }
                                Log.d(TAG, msg);
                                Toast.makeText(MainActivity.this, msg, Toast.LENGTH_SHORT).show();
                            }
                        });
                // [END subscribe_topics]
            }
        });

        binding.logTokenButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // Get token
                // [START log_reg_token]
                FirebaseMessaging.getInstance().getToken()
                    .addOnCompleteListener(new OnCompleteListener<String>() {
                        @Override
                        public void onComplete(@NonNull Task<String> task) {
                          if (!task.isSuccessful()) {
                            Log.w(TAG, "Fetching FCM registration token failed", task.getException());
                            return;
                          }

                          // Get new FCM registration token
                          String token = task.getResult();

                          // Log and toast
                          String msg = getString(R.string.msg_token_fmt, token);
                          Log.d(TAG, msg);
                          Toast.makeText(MainActivity.this, msg, Toast.LENGTH_SHORT).show();
                        }
                    });
                // [END log_reg_token]
            }
        });
    }