Question

contains有一个方便的/** * Returns {@code true} if this queue contains the specified element. * More formally, returns {@code true} if and only if this queue contains * at least one element {@code e} such that {@code o.equals(e)}. * * @param o object to be checked for containment in this queue * @return {@code true} if this queue contains the specified element * @throws ClassCastException if the class of the specified element * is incompatible with this queue * (<a href="../Collection.html#optional-restrictions">optional</a>) * @throws NullPointerException if the specified element is null * (<a href="../Collection.html#optional-restrictions">optional</a>) */ public boolean contains(Object o);方法：

predicate

我需要更具体一点：应用Using a ArrayBlockQueue Invoking toArray /搜索条件。

有没有办法做到这一点

{{1}}

那会有效..但如果队列很大怎么办？这可能会导致内存分配问题。

Answer 1

我不知道你应该这样做，但似乎你可以这样做：

Checking item 1 against predicate QueueEquals$Matcher$$Lambda$1/531885035@816f27d
Checking item 3 against predicate QueueEquals$Matcher$$Lambda$1/531885035@816f27d
Checking item 5 against predicate QueueEquals$Matcher$$Lambda$1/531885035@816f27d
Checking item 7 against predicate QueueEquals$Matcher$$Lambda$1/531885035@816f27d
Checking item 9 against predicate QueueEquals$Matcher$$Lambda$1/531885035@816f27d
Checking item 11 against predicate QueueEquals$Matcher$$Lambda$1/531885035@816f27d
Checking item 13 against predicate QueueEquals$Matcher$$Lambda$1/531885035@816f27d
false
Checking item 1 against predicate QueueEquals$Matcher$$Lambda$1/531885035@816f27d
Checking item 2 against predicate QueueEquals$Matcher$$Lambda$1/531885035@816f27d
true

输出：

hashCode()

它确实让我想要洗澡......另外，正如pvg正确指出的那样 - 这不能保证工作。在调用equals()之前，BlockingQueue实现可能会调用BlockingQueue，然后我们就会被搞砸。

一个更健全的选择是迭代阻塞队列，并针对每个元素运行谓词。 iterator接口没有ArrayBlockingQueue，但有许多阻塞队列实现，例如LinkedBlockingQueue和<packageCredentials>。

Answer 2

您可以直接在Queue上流式传输（如果您愿意，可以并行）并使用您的谓词过滤掉您的元素。 BlockingQueue是Queue，Collection，因此定义stream()和parallelStream()。以下内容：

public class SampleApplication {

    private static final int ELEMENT_COUNT = 100000;

    public static void main(String[] args) {
        Queue<Element> blockingQueue = new ArrayBlockingQueue<>(ELEMENT_COUNT);
        List<Element> elements = Stream.generate(SampleApplication::createElement).limit(ELEMENT_COUNT).collect(Collectors.toList());
        blockingQueue.addAll(elements);

        blockingQueue.stream().filter(getFilterPredicate(5)).findAny().ifPresent(System.out::println);
        blockingQueue.stream().filter(getFilterPredicate(105)).findAny().ifPresent(System.out::println);
        blockingQueue.stream().filter(getFilterPredicate(-1)).findAny().ifPresent(System.out::println);
    }

    private static Predicate<Element> getFilterPredicate(int value) {
        return e -> e.getId() == value;
    }

    private static int i = 0;
    private static Element createElement() {
        return new Element(++i);
    }

    static class Element {
        private int id;
        private String message;

        public Element(int id) {
            this.id = id;
            this.message = "Default msg";
        }

        //Getters, Setters & toString omitted
    }
}

输出以下值：

Element{id=5, message=Default msg}
Element{id=105, message=Default msg}

包含java.util.concurrent.BlockingQueue的谓词（/ find / search）？

2 个答案: