如何应对ConcurrentModificationException的(How to deal w

我从我的冷却时间得到一个ConcurrentModificationException的。我使用一个线程来降低每一秒这样的值：

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);
            }
        }
    }

}

所以每一秒钟就应减少每个球员20冷却时间，但问题是，我一个获得CME每几个小时运行程序时，尤其是当很多人在线。如何让这个如果它仍是修改列表，它会等待，直到当前操作完成，并创造一种修改队列？谢谢！这里是堆栈跟踪：

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......

Answer 1:

使用foreach循环时，您不能修改的集合。

但是，您可以遍历Map.entrySet()做你需要的一切：

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
        }
    }
}

Answer 2:

一个ConcurrentModificationException ，而你试图修改的内容被抛出Collection ，同时，在同一时间Iterating通过它。

阅读这和这有关它的更多讨论。

为什么有时它可能会制定出适合您的原因中明确提到的文档。

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.