This is a simple method which will create a Notification on Android.

MainActivity.java

private void createSimpleNotification() {
        NotificationCompat.Builder mBuilder =
                new NotificationCompat.Builder(this)
                        .setSmallIcon(R.mipmap.ic_launcher)
                        .setContentTitle("My notification")
                        .setContentText("Hello World!");
        // Creates an explicit intent for an Activity in your app
        Intent resultIntent = new Intent(this, MainActivity.class);

        // The stack builder object will contain an artificial back stack for the
        // started Activity.
        // This ensures that navigating backward from the Activity leads out of
        // your application to the Home screen.
        TaskStackBuilder stackBuilder = TaskStackBuilder.create(this);
        // Adds the back stack for the Intent (but not the Intent itself)
        stackBuilder.addParentStack(MainActivity.class);
        // Adds the Intent that starts the Activity to the top of the stack
        stackBuilder.addNextIntent(resultIntent);
        PendingIntent resultPendingIntent =
                stackBuilder.getPendingIntent(
                        0,
                        PendingIntent.FLAG_UPDATE_CURRENT
                );
        mBuilder.setAutoCancel(true);
        mBuilder.setContentIntent(resultPendingIntent);
        NotificationManager mNotificationManager =
                (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
        // mId allows you to update the notification later on.
        mNotificationManager.notify(101, mBuilder.build());
    }