迭代时从 HashSet 中删除元素 [英] Remove Elements from a HashSet while Iterating

问题描述

所以，如果我在迭代时尝试从 Java HashSet 中删除元素，我会得到 ConcurrentModificationException.如下例所示，从 HashSet 中删除元素子集的最佳方法是什么?

So, if I try to remove elements from a Java HashSet while iterating, I get a ConcurrentModificationException. What is the best way to remove a subset of the elements from a HashSet as in the following example?

Set<Integer> set = new HashSet<Integer>();

for(int i = 0; i < 10; i++)
    set.add(i);

// Throws ConcurrentModificationException
for(Integer element : set)
    if(element % 2 == 0)
        set.remove(element);

这是一个解决方案，但我认为它不是很优雅:

Here is a solution, but I don't think it's very elegant:

Set<Integer> set = new HashSet<Integer>();
Collection<Integer> removeCandidates = new LinkedList<Integer>();

for(int i = 0; i < 10; i++)
    set.add(i);

for(Integer element : set)
    if(element % 2 == 0)
        removeCandidates.add(element);

set.removeAll(removeCandidates);

谢谢！

推荐答案

您可以手动迭代集合的元素:

You can manually iterate over the elements of the set:

Iterator<Integer> iterator = set.iterator();
while (iterator.hasNext()) {
    Integer element = iterator.next();
    if (element % 2 == 0) {
        iterator.remove();
    }
}

你会经常看到这种模式使用 for 循环而不是 while 循环:

You will often see this pattern using a for loop rather than a while loop:

for (Iterator<Integer> i = set.iterator(); i.hasNext();) {
    Integer element = i.next();
    if (element % 2 == 0) {
        i.remove();
    }
}

正如人们所指出的，使用 for 循环是首选，因为它将迭代器变量(在本例中为 i)限制在较小的范围内.

As people have pointed out, using a for loop is preferred because it keeps the iterator variable (i in this case) confined to a smaller scope.

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