java - Java 中的 PriorityQueue 不是确定性的吗？

Question

当我运行以下优先级队列测试时:

class Run {

public static void main(String[] args) {
    PriorityQueue<Entry> q = new PriorityQueue<>(8, Collections.reverseOrder(new Comparator<Entry>() {

        @Override
        public int compare(Entry o1, Entry o2) {
            return Integer.compare(o1.getValue(), o2.getValue());
        }
    }));

    q.offer(new Entry(100));
    q.offer(new Entry(0));
    q.offer(new Entry(1));
    q.offer(new Entry(-1));
    q.offer(new Entry(0));
    q.offer(new Entry(1));
    q.offer(new Entry(-100));
    q.offer(new Entry(100));

    while (q.peek() != null) {
        System.out.println(q.poll());
    }
}

private static class Entry {

    private static int GLOBAL_ID = 0;

    private final int value, id;

    public Entry(int value) {
        this.value = value;
        id = GLOBAL_ID++;
    }

    public int getValue() {
        return value;
    }

    @Override
    public String toString() {
        return "Entry[" + id + ", value = " + value + ']';
    }
}

我得到以下结果:

Entry[0, value = 100]
Entry[7, value = 100]
Entry[2, value = 1]
Entry[5, value = 1]
Entry[4, value = 0]
Entry[1, value = 0]
Entry[3, value = -1]
Entry[6, value = -100]

我希望相同的元素以与输入相同的顺序输出，因此当在条目 7 之前提供条目 0 时，它也会在轮询 7 之前轮询。但为什么条目 4 突然在条目 1 之前被轮询？是错误的 Comparator 还是 PriorityQueue 不能保证确定性行为？

Answer 1

它是不确定的。

来自documentation for PriorityQueue

If multiple elements are tied for least value, the head is one of those elements -- ties are broken arbitrarily.