NotificationChannel | Android Developers Exploring Android O: Notification Channels

public class MyGcmListenerService extends GcmListenerService {

    private static final String TAG = "MyGcmListenerService";
    private NotificationManager notifManager;
    private NotificationChannel mChannel;

    /**     * Called when message is received.     *     

* @param from SenderID of the sender.    

 * @param data Data bundle containing message data as key/value pairs.    

 *             For Set of keys use data.keySet().   

  */    // [START receive_message]    @Override   

 public void onMessageReceived (String from, Bundle data) {
        String message = data.getString ("message");
        Log.d (TAG, "Message: " + message);

        sendNotification (message, message);

        // [END_EXCLUDE]    }
    // [END receive_message]
    /**     * Create and show a simple notification containing the 

received GCM message.     *   

  * @param message GCM message received.     */ 

   private void sendNotification (String message, String title) {
        Intent intent;
        PendingIntent pendingIntent;
        NotificationCompat.Builder builder;
        if (notifManager == null) {
            notifManager = (NotificationManager) getSystemService 

(Context.NOTIFICATION_SERVICE);
        }

        intent = new Intent (this, MainActivity.class);
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            int importance = NotificationManager.IMPORTANCE_HIGH;
            if (mChannel == null) {
                NotificationChannel mChannel = new NotificationChannel 

("0", title, importance);
                mChannel.setDescription (message);
                mChannel.enableVibration (true);
                mChannel.setVibrationPattern (new long[]

{100, 200, 300, 400, 500, 400, 300, 200, 400});
                notifManager.createNotificationChannel (mChannel);
            }
            builder = new NotificationCompat.Builder (this, "0");

            intent.setFlags (Intent.FLAG_ACTIVITY_CLEAR_TOP |

 Intent.FLAG_ACTIVITY_SINGLE_TOP);
            pendingIntent = PendingIntent.getActivity (this, 0, intent, 0);
            builder.setContentTitle (title)  // flare_icon_30             

       .setSmallIcon (R.mipmap.app_icon) // required                 

   .setContentText (message)  // required                

    .setDefaults (Notification.DEFAULT_ALL)
                    .setAutoCancel (true)
                    .setLargeIcon (BitmapFactory.decodeResource 

(getResources (), R.mipmap.app_icon))
                    .setBadgeIconType (R.mipmap.app_icon)
                    .setContentIntent (pendingIntent)
                    .setSound (RingtoneManager.getDefaultUri 

(RingtoneManager.TYPE_NOTIFICATION))
                    .setVibrate (new long[]{100, 200, 300, 400, 

500, 400, 300, 200, 400});
        } else {

            builder = new NotificationCompat.Builder (this);

            intent.setFlags (Intent.FLAG_ACTIVITY_CLEAR_TOP |

 Intent.FLAG_ACTIVITY_SINGLE_TOP);
            pendingIntent = PendingIntent.getActivity (this, 0, intent, 0);
            builder.setContentTitle (title)
                    .setSmallIcon (R.mipmap.app_icon) // required  

                  .setContentText (message)  // required            

        .setDefaults (Notification.DEFAULT_ALL)
                    .setAutoCancel (true)
                    .setContentIntent (pendingIntent)
                    .setSound (RingtoneManager.getDefaultUri 

(RingtoneManager.TYPE_NOTIFICATION))
                    .setVibrate (new long[]{100, 200, 300, 400, 500,

 400, 300, 200, 400})
                    .setPriority (Notification.PRIORITY_HIGH);
        } // else if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
        Notification notification = builder.build ();
        notifManager.notify (0, notification);
    }
}