将 ArrayList 嵌入式循环转换为迭代器

Question

我在获取使用迭代器背后的逻辑时遇到问题。我需要能够从循环内的 ArrayList 中删除元素，所以我想我会使用 Iterator 对象。但是，我不确定如何将原始代码转换为迭代器。

原始循环：

ArrayList<Entity> actorsOnLocation = loc.getActors();
int size = actorsOnLocation.size();

if (size > 1) {
    for(Entity actor: actorsOnLocation) {
        // Loop through remaining items (with index greater than current)
        for(int nextEnt=index+1; nextEnt < size-1; nextEnt++) {
            Entity opponent = actorsOnLocation.get(nextEnt);
            // Here it's possible that actor or opponent "dies" and
            // should be removed from the list that's being looped
        }
    }
}

我知道我必须使用 while 循环，它适用于第一个循环。但是如何将第二个循环的条件转换为与迭代器一起使用的条件？ This post 表示您可以在任何时候获取迭代器，但在 the documentation 我找不到诸如 .get 方法之类的任何东西。

ArrayList<Entity> actorsOnLocation = loc.getActors();
int size = actorsOnLocation.size();
Iterator actorsIterator = actorsOnLocation.iterator();

// How to get size of an iterator?
if (size > 1) {
    while(actorsIterator.hasNext()) {
        Entity actor = (Entity) actorsIterator.next();
        // How to get current index?
        int index = actorsIterator.indexOf(actor);
        // How to convert these conditions to Iterator?
        for(int nextEnt=index+1; nextEnt < size-1; nextEnt++) {
            Entity opponent = actorsOnLocation.get(nextEnt);
            // Here it's possible that actor or opponent "dies" and
            // should be removed from the list that's being looped

            // If the actor dies, the outer loop should skip to the next element
        }
    }
}

最后一个问题：如果您在迭代器中访问一个元素，该元素不是原始元素的副本，对吗？换句话说，我可以为该元素设置属性，然后通过访问原始 Collection 来访问这些更改的属性？

作为Eran pointed out，这可能不像看起来那么简单，因为两个循环遍历同一个列表并可能相互干扰。那么问题来了，我该如何解决这个问题呢？

Answer 1

演员或对手有可能“死亡”并应从列表中删除

你可以通过ListIterator<T>实现actor的移除，但是移除对手是非法的，因为actor的迭代器会失效。这会导致ConcurrentModificationException。

你需要改变你的算法：因为你需要从两个位置移除，你需要将内部循环而不是外部循环转换为使用迭代器：

outerLoop:
for(int i = 0 ; i < actorsOnLocation.length()-1 ; i++) {
    Entity actor = actorsOnLocation.get(i);
    // Loop through remaining items (with index greater than current)
    ListIterator<Entity> oppIter = actorsOnLocation.listIterator(i+1);
    while (oppIter.hasNext()) {
        Entity opponent = oppIter.next();
        // Here it's possible that actor or opponent "dies" and
        // should be removed from the list that's being looped
        if (opponent.mustDie()) {
            oppIter.remove();
        } else if (actor.mustDie()) {
            // The following operation invalidates oppIter
            actorsOnLocation.remove(i);
            // so we must continue the outer loop
            continue outerLoop;
        }
    }
}