使用iterator和iterator.remove（）时发生ConcurrentModificationException

Question

    private int checkLevel(String bigWord, Collection<String> dict, MinMax minMax)
{
    /*value initialised to losing*/
    int value = 0; 
    if (minMax == MinMax.MIN) value = 1; 
    else value = -1;


    boolean go = true;

    Iterator<String> iter = dict.iterator();

    while(iter.hasNext())
    {
        String str = iter.next(); 
        Collection<Integer> inds = naiveStringSearch(bigWord, str);

        if(inds.isEmpty())
        {
            iter.remove();
        }

        for (Integer i : inds)
        {
            MinMax passin = minMax.MIN;
            if (minMax == MinMax.MIN) passin = minMax.MAX;

            int value2 = checkLevel(removeWord(bigWord, str, i), dict, passin); 
            if (value2 == -1 && minMax == minMax.MIN)
            {
                value = -1; 
                go = false;
            }
            if (value2 == 1 && minMax == minMax.MAX)
            {
                value = 1; 
                go = false; 
            }

        }

        if (go == false) break; 
    }


    return value;
}

错误：

Exception in thread "main" java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.nextEntry(HashMap.java:810)
at java.util.HashMap$KeyIterator.next(HashMap.java:845)
at aStringGame.Main.checkLevel(Main.java:67)
at aStringGame.Main.test(Main.java:117)
at aStringGame.Main.main(Main.java:137)

这是什么问题

Answer 1

某处正在修改dict。我怀疑它可能在此调用内发生：

int value2 = checkLevel(removeWord(bigWord, str, i), dict, passin);
                                                     ^^^^

编辑 基本上，发生的是通过 另一个 迭代器进行的递归checkLevel()修改。这使得外部迭代器的故障快速行为得以解决。dict __