如何自定义PriorityQueue.stream().foreach以优先级顺序进行迭代

本文介绍了如何自定义PriorityQueue.stream().foreach以优先级顺序进行迭代的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我有一个带有PriorityQueue字段的类:

I have a class with PriorityQueue field inside:

public class MyClass<T>{ Queue<T> queue = new PriorityQueue<>();

我想以某种方式从MyClass获取流并使用foreach，并希望序列按PriorityQueue的优先级顺序运行.最简单的方法是重写stream()方法:

I want somehow get a stream from MyClass and use foreach and want the sequence behave in priority order of my PriorityQueue. The easiest way is to override stream() method:

@Override public Stream stream() { return queue.stream(); }

，但这不会按优先级顺序显示队列元素.因此，问题是:如何使foreach流方法的行为类似于:

but this will not expose the queue element in priority order. So the question is: how to make foreach stream method behave like:

while(!queue.isEmpty()) queue.poll();

推荐答案

您可以使用 Stream :: generate 和"> Queue :: poll 方法来创建 Stream ，其中包含 PriorityQueue 中的元素并保持其顺序:

You could use Stream::generate and Queue::poll method to get create a Stream with elements from PriorityQueue with keeping their order:

@Override public Stream<T> stream() { return Stream.generate(queue::poll); }

但是这可能很危险，因为 Stream :: generate 将不断调用 poll ，因此它可能是无限的Stream.因此，应考虑在队列大小中使用 Stream :: limit :

However this might be dangerous because Stream::generate will be invoking poll constantly so it is potentially an inifinite Stream. Therfore using Stream::limit with the queue size should be considered :

@Override public Stream<T> stream() { return Stream.generate(queue::poll) .limit(queue.size()); }

或者您可以简单地返回已排序的流:

Or you could simply return sorted stream :

@Override public Stream<T> stream() { return queue.stream() .sorted(comparator); }

比较器是您的比较器.

在 Java 9 中，您可以使用 Stream :: takeWhile ，其谓词拒绝空值.因为当队列为空时， Queue :: poll 将返回 null -生成的 Stream 将按顺序包含队列中的元素(这是替代方法)如第一个解决方案所述使用 limit ):

In Java 9 you could use Stream::takeWhile with predicate that rejects nulls. As Queue::poll will return null when queue is empty - the resulting Stream will contain elements from the queue in their order (this is alternative to using limit as described in the first solution) :

@Override public Stream<T> stream() { return Stream.generate(queue::poll) .takeWhile(Objects::nonNull); }