java - 无法理解 PriorityQueue 如何改变排序顺序？

Question

import java.util.*;
class abc {

    public static void main(String args[]){

        PriorityQueue<Integer> pq = new PriorityQueue<Integer>();

        pq.add(1);
        pq.add(2);
        pq.add(3);
        pq.add(4);
        pq.add(5);
        pq.add(6);

        System.out.println(pq);
        pq.remove();
        System.out.println(pq);     
    }           
}

当我删除元素时，顺序会改变。输出应根据字典排序按升序排列。但是我得到的输出是:

Answer 1

调用 System.out.println(pq); 等同于调用 System.out.println(pq.toString());

如果您查看 documentation of the the toString() method ，您会看到它指出:

Returns a string representation of this collection. The string representation consists of a list of the collection's elements in the order they are returned by its iterator, enclosed in square brackets ("[]"). Adjacent elements are separated by the characters ", " (comma and space). Elements are converted to strings as by String.valueOf(Object).

我突出了重要的部分。所以我们需要看看 documentation of the iterator of the priority queue其中指出:

Returns an iterator over the elements in this queue. The iterator does not return the elements in any particular order.

因此您的代码的输出不允许对优先级队列强加的顺序作出任何结论。

在main documentation of the PriorityQueue它说:

The Iterator provided in method iterator() is not guaranteed to traverse the elements of the priority queue in any particular order. If you need ordered traversal, consider using Arrays.sort(pq.toArray()).