When construct PriorityQueue, you specify a Comparator to determine the order.
In JDK8, with lambda, you can do it like this,
private PriorityQueue<Packet> packetQueue = new PriorityQueue<>((p1, p2) ->
p1.getPacketId() == specified_id ? -1 : 0);
This gives specified_id a boost while others remains same. Implement your prioritization in the Comparator.