如何在沒有ConcurrentModificationException的情況下刪除List迭代

Question

我的allWordsList類似於： [aaa, bbb, ccc, ddd, eee]

如何進行復印（ tempWordsList的） allWordsList在

for (String aWord : aWordsList) 

沒有迭代項（即實現[bbb, ccc, ddd, eee] ，然后[aaa, ccc, ddd, eee]等）？

public class Anagrams {

    List<String> allWordsList = new ArrayList<String>();
    List<List<String>> myList = new ArrayList<List<String>>();
    List<String> tempWordsList = new ArrayList<String>();

    public Anagrams(String allWords) {
        getWordsList(allWordsList, allWords); // getting List to copy here
        getAnagramWordsList(allWordsList);
    }

    private void getAnagramWordsList(List<String> aWordsList) {
        for (String aWord : aWordsList){
            //tempWordsList.clear();
            tempWordsList = aWordsList;
            for (Iterator<String> iterator = tempWordsList.iterator(); iterator.hasNext();) {
                String string = iterator.next();
                if (string == aWord) {
                    // Remove the current element from the iterator and the list.
                    iterator.remove();
                }
            }
            myList.add(tempWordsList);
            System.out.println(aWordsList);
            System.out.println(tempWordsList); //before error both lists are without first item...
        }
    }

}

我經歷了幾個類似的案例，但仍然不太了解。

Answer 1

您的代碼中最大的問題是tempWordsList和aWordsList引用同一對象。 您對tempWordsList任何更改aWordsList在同一確切時間發生在aWordsList上：

tempWordsList = aWordsList;

因此， myList會有最后修改的多個副本aWordList ：

myList.add(tempWordsList);

在循環的每次迭代中將相同的對象添加到myList中。

為了制作aWordsList和tempWordsList您需要用一個副本替換賦值，如下所示：

tempWordsList = new List<String>(aWordsList);

Answer 2

應該是這樣的：

Iterator<String> it = tempWordsList.iterator();
while(it.hasNext()){
    String value = it.next();
   // System.out.println("List Value:"+value);
   if (value.equals(aWord)) {
      it.remove();
        }
    }

Answer 3

解決問題的方法如下，但這並不是一個好的解決方法。

//解決

private void getAnagramWordsList(List<String> aWordsList) {

    List<Integer> toRemove = new ArrayList<Integer>();

    for (String aWord : aWordsList){
        //tempWordsList.clear();
        tempWordsList = aWordsList;

        for (int i = tempWordsList.size()-1; i > 0; i--) {
            if (string.equals(tempWordsList.get(i)) {
                toRemove.add(i);
            }
        }
        for(int idx = 0; idx < toRemove.size(); idx++)
          tempWordsList.remove(idx);

        myList.add(tempWordsList);

        System.out.println(aWordsList);
        System.out.println(tempWordsList); //before error both lists are without first item...
    }