How to show Heads up notifications android

How to get a heads up notification.With below code i can only see three dots on status bar and a notification in notification bar.

Intent intent = new Intent(this, MainActivity.class);

intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
PendingIntent pendingIntent = PendingIntent.getActivity(this, 0 , intent,PendingIntent.FLAG_ONE_SHOT);
Bitmap bm = BitmapFactory.decodeResource(getResources(), R.drawable.bip);
Uri defaultSoundUri=RingtoneManager.getDefaultUri(RingtoneManager.TYPE_NOTIFICATION);
NotificationCompat.Builder notificationBuilder = new NotificationCompat.Builder(this)
                .setSmallIcon(R.drawable.bip)
                .setContentTitle("Temp")
                .setPriority(NotificationCompat.PRIORITY_HIGH)
                .setContentText(message)
                .setAutoCancel(true)
                .setSound(defaultSoundUri)
                .setContentIntent(pendingIntent);

NotificationManager notificationManager =
                (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);

notificationManager.notify(0, notificationBuilder.build());

Answer

I was having the same problem, but I was using the newer NotificationCompat.Builder() call which requires a channel ID from a NotificationChannel.

The notification will only appear as a heads-up notification if the NotificationChannel is created with an importance value of NotificationManager.IMPORTANCE_HIGH:

NotificationChannel channel = new NotificationChannel("channel01", "name", 
     NotificationManager.IMPORTANCE_HIGH);   // for heads-up notifications
channel.setDescription("description");

// Register channel with system
NotificationManager notificationManager = getSystemService(NotificationManager.class);
notificationManager.createNotificationChannel(channel);

Show the heads-up notification:

Notification notification = new NotificationCompat.Builder(this, "channel01")
        .setSmallIcon(android.R.drawable.ic_dialog_info)
        .setContentTitle("Test")
        .setContentText("You see me!")
        .setDefaults(Notification.DEFAULT_ALL)
        .setPriority(NotificationCompat.PRIORITY_HIGH)   // heads-up
        .build();

NotificationManagerCompat notificationManager = NotificationManagerCompat.from(this);
notificationManager.notify(0, notification);