迭代通过集合，避免ConcurrentModificationException在循环中删除 [英] Iterating through a Collection, avoiding ConcurrentModificationException when removing in loop

问题描述

我们都知道你不能这样做：

We all know you can't do this:

for (Object i : l) {
    if (condition(i)) {
        l.remove(i);
    }
}

ConcurrentModificationException 等...这显然工作有时，但不总是。下面是一些具体代码：

ConcurrentModificationException etc... this apparently works sometimes, but not always. Here's some specific code:

public static void main(String[] args) {
    Collection<Integer> l = new ArrayList<Integer>();

    for (int i=0; i < 10; ++i) {
        l.add(new Integer(4));
        l.add(new Integer(5));
        l.add(new Integer(6));
    }

    for (Integer i : l) {
        if (i.intValue() == 5) {
            l.remove(i);
        }
    }

    System.out.println(l);
}

这当然会导致：

Exception in thread "main" java.util.ConcurrentModificationException

b $ b

...即使多个线程没有这样做...无论如何。

... even though multiple threads aren't doing it... Anyway.

这个问题的最佳解决方案是什么？如何从循环中的集合中删除项目，而不抛出此异常？

What's the best solution to this problem? How can I remove an item from the collection in a loop without throwing this exception?

我也使用任意的集合这里，不一定是 ArrayList ，所以你不能依赖 get 。

I'm also using an arbitrary Collection here, not necessarily an ArrayList, so you can't rely on get.

推荐答案

Iterator.remove（）是安全的，你可以这样使用： p>

Iterator.remove() is safe, you can use it like this:

List<String> list = new ArrayList<>();

// This is a clever way to create the iterator and call iterator.hasNext() like
// you would do in a while-loop. It would be the same as doing:
//     Iterator<String> iterator = list.iterator();
//     while (iterator.hasNext()) {
for (Iterator<String> iterator = list.iterator(); iterator.hasNext();) {
    String string = iterator.next();
    if (string.isEmpty()) {
        // Remove the current element from the iterator and the list.
        iterator.remove();
    }
}

注意 Iterator.remove 是在迭代期间修改集合的唯一安全方法;

Note that Iterator.remove is the only safe way to modify a collection during iteration; the behavior is unspecified if the underlying collection is modified in any other way while the iteration is in progress.

来源：

http://docs.oracle.com/javase/tutorial /collections/interfaces/collection.html

同样，如果您有 ListIterator ，并且想要添加项目，您可以使用 ListIterator＃add ，出于同样的原因，您可以使用 Iterator＃remove  —它的设计允许它。

And similarly, if you have a ListIterator and want to add items, you can use ListIterator#add, for the same reason you can use Iterator#remove — it's designed to allow it.

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