1

我从我的冷却计时器中获得了 ConcurrentModificationException。我使用一个线程来减少每秒的值，如下所示：

public class CoolDownTimer implements Runnable {
    @Override
    public void run() {
        for (String s : playerCooldowns.keySet()) {
            playerCooldowns.put(s, playerCooldowns.get(s) - 20);
            if (playerCooldowns.get(s) <= 0) {
                playerCooldowns.remove(s);
            }
        }
    }

}

所以每秒它应该将每个玩家的冷却时间减少 20，但问题是我在运行程序时每隔几个小时就会获得一次 CME，尤其是当很多人在线时。我该如何做到这一点，如果它仍在修改列表，它将等到当前操作完成并创建一种修改队列？谢谢！这是堆栈跟踪：

2012-06-18 20:59:05 [WARNING] Task of 'SurvivorsClasses' generated an exception
java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.nextEntry(HashMap.java:839)
at java.util.HashMap$KeyIterator.next(HashMap.java:874)
at me.zachoooo.survivorclasses.CoolDownManager$CoolDownTimer.run(CoolDownManager.java:13)
at org.bukkit.craftbukkit.scheduler.CraftScheduler.mainThreadHeartbeat(CraftScheduler.java:126)
at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:533)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:459)

第 13 行是 for 循环的开始...

4

3 回答 3

3

使用 foreach 循环时不能修改集合。

但是，您可以迭代Map.entrySet()并执行所需的一切：

public void run() {
    for (Iterator<Map.Entry<String,Integer>> i = playerCooldowns.entrySet().iterator(); i.hasNext();) {
        Map.Entry<String,Integer> entry = i.next();
        entry.setValue(entry.getValue() - 20); // update via the Map.Entry
        if (entry.getValue() <= 0) {
            i.remove(); // remove via the iterator
        }
    }
}
于 2012-06-19T04:31:55.097 回答
1

ConcurrentModificationException当您尝试修改 的内容时抛出A Collection，同时Iterating通过它。

阅读this和this以获得更多讨论。

文档中清楚地提到了有时它可能对您有用的原因。

The iterators returned by all of this class's "collection view methods" are fail-fast: if 
the map is structurally modified at any time after the iterator is created, in any way 
except through the iterator's own remove method, the iterator will throw a 
ConcurrentModificationException. Thus, in the face of concurrent modification, the 
iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic 
behavior at an undetermined time in the future.

Note that the fail-fast behavior of an iterator cannot be guaranteed as it is, generally 
speaking, impossible to make any hard guarantees in the presence of unsynchronized 
concurrent modification. Fail-fast iterators throw ConcurrentModificationException on a 
best-effort basis.
于 2012-06-19T04:22:44.993 回答
0

Unlike Array，Collections仅在编译时检查，而不是在运行时检查，这就是你不能像循环中的 put() 或 remove() 那样修改 Collection 的原因。

于 2012-06-19T04:35:33.377 回答