PriorityQueue没有在添加上排序

问题描述

我有一个优先级队列，我在其中添加一个Node对象，其中节点应按其包含的值进行排序。出于某种原因，优先级队列不会对添加的节点进行排序。如果有人可以看到这个问题或有任何指导，我很感激。这是一个简短的例子：

I have a Priority Queue in which I add a Node object to, where the Nodes should be sorted by a value that they contain. For some reason, the priority queue will not sort the Nodes on add. If anyone can see something wrong with this or has any guidance, I appreciate it. Here is a brief example:

PriorityQueue<Node> PQ = new PriorityQueue<Node>();
        //for each entry create a node and add it to the PriorityQueue
        for(Entry<Character,Integer> entry : entries){
            PQ.add(new Node(entry.getKey(),entry.getValue(), true));
        }

这里是节点的 compareTo 方法：

@Override
public int compareTo(Node n) {
  if(n.frequency.intValue() > this.frequency.intValue()) return  -1;
  else if(n.frequency.intValue() == this.frequency.intValue()) return 0;
  else return 1;
}

推荐答案

我猜您期望 PriorityQueue 在迭代时以特定顺序返回元素。但是， PriorityQueue 不提供这样的行为，因为它是作为优先级堆而不是排序列表实现的。来自：

I guess you expect PriorityQueue to return elements in particular order when you iterate it. However, PriorityQueue doesn't provide such a behaviour, because it's implemented as a priority heap rather than sorted list. From javadoc:

PriorityQueue 提供的唯一保证是 poll（）， peek（）等返回最少的元素。如果您需要对元素进行有序迭代，请使用其他集合，例如 TreeSet 。

The only guarantee provided by PriorityQueue is that poll(), peek(), etc return the least element. If you need ordered iteration of elements, use some other collection such as TreeSet.

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