Java中的ContainsAll的成本是多少? [英] What is the cost of ContainsAll in Java?

问题描述

我今天在一些编码中发现了containsAll()(一种List接口方法)，它看起来很漂亮.有谁知道在性能/迭代方面要花多少钱?

I discovered containsAll() (a List interface method) during some coding today, and it looks pretty slick. Does anyone know how much this costs in terms of performance/iterations?

文档并没有提供太多帮助.

The documentation didn't offer much in terms of that.

推荐答案

• 首先，迭代提供的集合中的每个元素
• 然后迭代列表的所有元素，并使用.equals(..)将当前元素与它们进行比较(注意:正如您在问题中所指定的，这是关于列表的.其他集合的行为有所不同)
• first, it iterates each element of the supplied collection
• then it iterates all elements of the list and compares the current element with them using .equals(..) (Note: this is about lists, as you specified in the question. Other collections behave differently)

所以它是O(n * m)，其中n和m是两个集合的大小.

So it's O(n*m), where n and m are the sizes of both collections.

public boolean containsAll(Collection<?> c) {
    Iterator<?> e = c.iterator();
    while (e.hasNext())
        if (!contains(e.next()))
        return false;
    return true;
}

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