在Java中为PriorityQueue（node）设置比较器

Question

If I have a node with two data variables.

Say

class HuffNode{
public char iData;
public int frequency;
public HuffNode leftChild;
public HuffNode rightChild;
// ---------------------------------------------------------
HuffNode(char d){
    this.iData = d;
    this.frequency = 0;
}
}

Then, I want to put them in ascending order into a priority que by each Node's frequency.

PriorityQueue<HuffNode> q = new PriorityQueue<HuffNode>();
    Set<Character>keys = map.keySet(); //iterator
    Iterator<Character> it = keys.iterator();
    while(it.hasNext()){
        char key = it.next();
        HuffNode node = new HuffNode(key);
        node.frequency = map.get(key);
        q.add()// want to add by frequency
    }

If I just add the nodes into the que, I think the nodes will end up in an alphabetical order. How can I change the comparator to the frequency ?

thank you in advance.

Answer 1

Pass a Comparator as a constructor parameter , eg

new PriorityQueue<>(
    initialCapacity,
    new Comparator<HuffNode>() {
      @Override public int compare(HuffNode a, HuffNode b) {
        return Integer.compare(a.frequency, b.frequency);
      }
    });

Note that you don't really want the thing you are using to order the nodes to be mutable, especially if it is public - if you were to change the frequency value, it wouldn't automatically reorder in the queue.

You'd be well-served making as many fields as possible final .