PriorityQueue是否允许重新排序队列中已有的元素？ [英] Does a PriorityQueue allow elements already within the queue to be reordered?

问题描述

我希望增加或降低 PriorityQueue 中项目的优先级：例如，我可能正在下载一长串图片，突然想要第三十个图片最高优先级。

I want to augment or lower the priority of items in a PriorityQueue: for example, I might be downloading a long list of images and suddenly want the thirtieth one to have highest priority.

据我所知， poll（）始终返回值最小的队列对象（如由比较器确定）。如果我可以降低队列中已有项的值（例如，如果该值由对象中的 int 确定，我会减少 int 某些其他函数中的值），它将首先由 poll（）返回，还是允许 poll的排序（）在插入时完成此操作（例如，将新队列元素向下列入列表直到达到自然深度）？

As I understand it, poll() always returns the queue object with the lowest value (as determined by a comparator). If I can lower the value of an item already in a queue (e.g. if this value is determined by an int in the object and I reduce the int value in some other function), will it be returned first by poll(), or is the sorting that allows poll() to do this done at insert time (e.g. by bubbling new queue elements down a list till they reach their "natural" depth)?

如果这是在 PriorityBlockingQueue 上完成的，是否会导致并发问题？

If this is done on a PriorityBlockingQueue, could it cause concurrency issues?

推荐答案

如果更改确定其顺序的属性，则Java中的任何集合都不会自动重新排序元素。对于依赖于.hashCode（）,. equals（）或某个比较器的集合，不允许在对象驻留在集合中时更改该对象，以便hashcode / equals或比较器产生不同的值。

None of the collections in Java automatically reorders elements if you change the property that determine their order. For collections that depend on the .hashCode() , .equals() or some comparator, you are not allowed to change the object while it resides in the collection so that the hashcode/equals or comparator would yield different values.

如果要在PriorityQueue中更改其优先级，则必须删除，更改，重新插入对象。

You have to remove, change, re-insert the object if you want to change its priority within a PriorityQueue.

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