ConcurrentModificationException（Java） [英] ConcurrentModificationException (Java)

问题描述

Exception in thread "main" java.util.ConcurrentModificationException
Squash the PC dirties the room Violet. The room's state is now dirty
Lily the animal growls
The Animal Lily left the room and goes to Green through the west door.
        at java.util.HashMap$HashIterator.nextEntry(HashMap.java:793)
        at java.util.HashMap$KeyIterator.next(HashMap.java:828)
        at homework5.Room.critReactRoomStateChange(Room.java:76)
        at homework5.PC.play(PC.java:121)
        at homework5.Main.main(Main.java:41)
Java Result: 1

这是我收到的错误。

我的方法看起来像

public void critReactRoomStateChange(String command, PC pc) {
    Creature temp = null;
    Iterator iterator = getCreatures().keySet().iterator();
    while (iterator.hasNext()) {
        String names = iterator.next().toString();
        if (!(getCreatures().get(names) instanceof PC)) {
            temp = getCreatures().get(names);
            if (temp != null) {
                temp.reactStateChange(command, pc);
                temp.checkNewRoom();
            }
        }
    }
} 

所以我理解的是这意味着我在迭代器完成之前就改变了它的大小，这就是你得到的错误。这是正确的，因为reactStateChange之一是将对象从hashMap中删除。我如何安全地执行此操作，以便在我删除某些内容时让Iterator提前知道，以便我可以避免此错误。提前致谢。如果需要更多细节，我很乐意满足您的要求。

So what I understand is this means I'm changing the size of the iterator before it is finished and this is the error you get. This is true as one of the reactStateChange is for an object to be removed out of the hashMap. How do I do this safely so that when I remove something it lets the Iterator know ahead of time so I can avoid this error. Thanks in advance. If more details are needed I'd be glad to meet your requests.

推荐答案

从基础集合中删除元素并继续迭代的唯一安全方法是使用 remove（） Iterator 的c $ c> 方法。这将删除 Iterator 的 next（）方法返回的最后一个元素。

The only safe way to remove an element from an underlying collection and continue the iteration is to use the remove() method of the Iterator. This removes the last element returned by the next() method of the Iterator.

在你的情况下，似乎这需要将 Iterator 传递给执行修改的方法（或使其成为实例字段，如 Map 对象已经存在）。

In your case, it appears that this would require passing the Iterator to the method that performs the modification (or make it an instance field, like the Map object is already).

这篇关于ConcurrentModificationException（Java）的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！