使用iterator和iterator.remove（）时出现ConcurrentModificationException [英] ConcurrentModificationException when using iterator and iterator.remove()

问题描述

    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)

这里有什么问题？

推荐答案

某处某处正在修改 dict 。我怀疑它可能会在这个调用中发生：

Something somewhere is modifying dict. I suspect it might be happening inside this call:

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

编辑基本上，会发生什么递归调用 checkLevel（）通过另一个迭代器修改 dict 。这使得外部迭代器的快速失败行为成为可能。

edit Basically, what happens is that the recursive call to checkLevel() modifies dict through another iterator. This makes the outer iterator's fail-fast behaviour to kick in.

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