我可以在 Java 中使用优先队列而不实现比较器吗？

Question

如果我想创建节点的优先级队列，并且每个节点只有一个字段（即int val ），我是否必须为优先级队列编写一个比较器？

Answer 1

Yes. Assuming your Node class is your custom class, Java does not know how to compare two Nodes even if there's but one field in it. Therefore, you will need to do

class Node implements Comparable<Node> {
    @Override
    public compareTo(Node other) {
        ...
    }
}

Answer 2

The elements of the priority queue are ordered according to their natural ordering, or by a Comparator . If you don't want to use Comparator then implement Comparable in your Node class.

Answer 3

No Comparator necessary. You can create a PriorityQueue that relies on a class's "natural ordering".

Creates a PriorityQueue with the default initial capacity (11) that orders its elements according to their natural ordering .

That links to Comparable . Make your Node class implement Comparable<Node> . Then you can use a PriorityQueue without a Comparator .

Answer 4

You don't necessarily need to implement Comparator in the Node class. You can use lambda expressions as detailed in the first part of this answer . I will modify that answer to fit into your question. For this to work you will have to create a getter method for the field that you have. Assuming that method is called "getVal()" This should work without needing to implement Comparator.

PriorityQueue<Node> pq=
            new PriorityQueue<Node>(Comparator.comparing(Node::getVal));