我无法弄清楚这个ConcurrentModificationException(I can't figure out this ConcurrentModificationException)

 我觉得我的Java生锈了，所以我尝试了一个简单的问题：使用链接列表进行合并排序，只返回唯一值。 以下是我的第一次尝试之一。 这对我来说很有意义。 问题是，无论我做了什么，我总是得到一个ConcurrentModificationException 。 
 
 我尝试过的事情包括： 
 
 
 
 使块或方法synchronized 。 
 
 
 用sort方法中的迭代器替换LinkedLists。 
 
 
 在单独的变量中跟踪列表的大小（该部分留在其中）。 
 
 
 没有任何效果。 ConcurrentModificationsException移动到其他地方但它仍然存在。 我真的不确定为什么。 我怎样才能解决这个问题？ 
 
 在此特定尝试中，异常发生在调用addAll 。 我把列表中的所有操作都放在了自己的块中，但是Java显然并不关心。 
 
package com.regularoddity.dotcloud;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;

public class Merge {

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        List<Integer> myList = new LinkedList<Integer>();
        myList.add(2);
        myList.add(9);
        myList.add(1);
        myList.add(3);
        myList.add(8);
        myList.add(7);
        myList.add(1);
        myList = sort(myList);
        Iterator<Integer> lit = myList.iterator();
        while(lit.hasNext()) System.out.printf("%s ", lit.next());
    }

    private static List<Integer> merge(List<Integer> list1, List<Integer> list2) {
        List<Integer> result = new LinkedList<Integer>();
        int size1 = list1.size();
        int size2 = list2.size();
        {
            while (size1 > 0 && size2 > 0) {
                if (list1.get(0) == list2.get(0)) {
                    result.add(list1.remove(0));
                    list2.remove(0);
                    size1--; size2--;
                }
                else if (list1.get(0) <= list2.get(0))
                {
                    result.add(list1.remove(0));
                    size1--;
                }
                else
                {
                    result.add(list2.remove(0));
                    size2--;
                }
            }
        }
        result.addAll(list1);
        result.addAll(list2);
        return result;
    }

    private static List<Integer> sort(List<Integer> list) {
        int lsize = list.size();
        if (lsize <= 1) return list;
        int pivot = lsize / 2;
        List<Integer> list1 = list.subList(0, pivot);
        List<Integer> list2 = list.subList(pivot, lsize);
        list1 = sort(list1);
        list2 = sort(list2);
        return merge(list1, list2);
    }


}
 
 让我感到困惑的是我从未明确地与列表进行交互。 必须有一个隐式迭代，但我似乎无法将其分解出来。 
 
 编辑：我没有包括堆栈跟踪，因为我（愚蠢地）认为，因为它为每次修复尝试而改变，所以它没有用。 但是，实际上，它没有太大变化。 这是当前实现的堆栈跟踪： 
 
Exception in thread "main" java.util.ConcurrentModificationException
    at java.util.SubList.checkForComodification(AbstractList.java:752)
    at java.util.SubList.size(AbstractList.java:625)
    at com.regularoddity.dotcloud.Merge.merge(Merge.java:30)
    at com.regularoddity.dotcloud.Merge.sort(Merge.java:64)
    at com.regularoddity.dotcloud.Merge.sort(Merge.java:62)
    at com.regularoddity.dotcloud.Merge.main(Merge.java:23)
 
 com.regularoddity.dotcloud.Merge.main（Merge.java:23） 

I was feeling my Java was rusty, so I tried a simple problem: a merge sort with Linked Lists that only returns unique values. Below was one of my first attempts. It made sense to me. The problem was, no matter what I did, I always got a ConcurrentModificationException.
 
Things I've tried include:
 
 
 
Making blocks or methods synchronized.
 
 
Replacing the LinkedLists with Iterators inside the sortmethod.
 
 
Keeping track of the size of the lists in separate variables (that part was left in).
 
 
Nothing worked. The ConcurrentModificationsException moved to other places but it remained in place. I'm really not sure why. How can I fix this?
 
In this particular attempt, the exception occurs at the call to addAll. I put all the operations on the lists inside their own block, but Java obviously doesn't care.
 
package com.regularoddity.dotcloud;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;

public class Merge {

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        List<Integer> myList = new LinkedList<Integer>();
        myList.add(2);
        myList.add(9);
        myList.add(1);
        myList.add(3);
        myList.add(8);
        myList.add(7);
        myList.add(1);
        myList = sort(myList);
        Iterator<Integer> lit = myList.iterator();
        while(lit.hasNext()) System.out.printf("%s ", lit.next());
    }

    private static List<Integer> merge(List<Integer> list1, List<Integer> list2) {
        List<Integer> result = new LinkedList<Integer>();
        int size1 = list1.size();
        int size2 = list2.size();
        {
            while (size1 > 0 && size2 > 0) {
                if (list1.get(0) == list2.get(0)) {
                    result.add(list1.remove(0));
                    list2.remove(0);
                    size1--; size2--;
                }
                else if (list1.get(0) <= list2.get(0))
                {
                    result.add(list1.remove(0));
                    size1--;
                }
                else
                {
                    result.add(list2.remove(0));
                    size2--;
                }
            }
        }
        result.addAll(list1);
        result.addAll(list2);
        return result;
    }

    private static List<Integer> sort(List<Integer> list) {
        int lsize = list.size();
        if (lsize <= 1) return list;
        int pivot = lsize / 2;
        List<Integer> list1 = list.subList(0, pivot);
        List<Integer> list2 = list.subList(pivot, lsize);
        list1 = sort(list1);
        list2 = sort(list2);
        return merge(list1, list2);
    }


}
 
The thing that baffles me the most is that I never explicitly interate over the list. There must be an implicit iteration going on, but I don't seem to be able to factor it out.
 
EDIT: I didn't include the stacktrace because I (foolishly) thought that as it changed for every attempt at a fix, it would not be useful. But, really, it doesn't change much. Here's the stacktrace for the current implementation:
 
Exception in thread "main" java.util.ConcurrentModificationException
    at java.util.SubList.checkForComodification(AbstractList.java:752)
    at java.util.SubList.size(AbstractList.java:625)
    at com.regularoddity.dotcloud.Merge.merge(Merge.java:30)
    at com.regularoddity.dotcloud.Merge.sort(Merge.java:64)
    at com.regularoddity.dotcloud.Merge.sort(Merge.java:62)
    at com.regularoddity.dotcloud.Merge.main(Merge.java:23)
 
com.regularoddity.dotcloud.Merge.main(Merge.java:23)

原文：https://stackoverflow.com/questions/16781136