维护 PriorityQueue 中的条目顺序

发布于 2024-11-10 03:52:16 字数 810 浏览 3 评论 0原文

我正在尝试使用 Java 中的 PriorityQueue。

我有一些自定义对象，并以这种方式将它们添加到队列中：

Pet pet1 = new Pet();
Pet pet2 = new Pet();
Pet pet3 = new Pet();

PriorityQueue<Pet> queue = new PriorityQueue<Pet>();
queue.offer(pet1);
queue.offer(pet2);
queue.offer(pet3);

此时，我意识到我的 Pet 对象必须实现 Comparable，以免从 PriorityQueue 获取 ClassCastException。所以我让我的 Pet 实现了 Comparable，然后重写了 copmareTo(obj) 方法，只返回 0。

但奇怪的是这里。当我...

queue.poll();  //return: pet1  queue: pet3, pet2
queue.poll();  //return: pet3  queue: pet2

既然我已经按照 pet1、pet2 和 pet3 的顺序添加了它们，为什么在我第一次调用 poll() 时，它会对我的 pet 序列进行排序？那么这整个事情就不再是一个队列了，因为它的进入顺序没有被保留，不是吗？

我怀疑这可能与 Comparable 接口和compareTo(obj) 方法有关。但我所需要的只是让它保持其输入顺序，因此我实际上不需要比较任何内容或对任何内容进行排序。

如何维护其在队列中的进入顺序？

谢谢！

原文

I am trying to make use of the PriorityQueue in Java.

I have a few custom objects and I add them into the queue this way:

Pet pet1 = new Pet();
Pet pet2 = new Pet();
Pet pet3 = new Pet();

PriorityQueue<Pet> queue = new PriorityQueue<Pet>();
queue.offer(pet1);
queue.offer(pet2);
queue.offer(pet3);

At this point, I realise that my Pet objects must implement Comparable in order not to get ClassCastException from PriorityQueue. So I had my Pet implements Comparable, and then override the copmareTo(obj) method with just return 0.

But the weird thing is this here. When I...

queue.poll();  //return: pet1  queue: pet3, pet2
queue.poll();  //return: pet3  queue: pet2

Since I had added them in the order of pet1, pet2 and pet3, why on my first call to poll(), it sorted my pet sequences? Then this whole thing becomes no longer a queue anymore since its entry sequence isn't preserved, isn't it?

I suspect it may have to do with the Comparable interface and compareTo(obj) method. But all I needed is for it to maintain its entry sequence, so I don't really need to compare anything or sort anything at all.

How can I maintain its entry sequence in the queue?

Thanks!

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