为了澄清 - 我不想从ArrayList中删除任何内容。因此，我发现的所有答案中有90％实际上并不适用。我在这里找不到任何东西，或者在其他地方找不到任何东西！
我正在编写一个Java应用程序来玩Hangman，其中对手（计算机）基本上是作弊，在某种意义上它不“选择”一个单词，它有一组单词并决定玩家的猜测是否正确或者不正确，取决于哪一个留下了更难以猜测的词组。
简而言之，我的问题是：
我有一个ArrayList，masterList，其中我有一组单词，如果你愿意的话，还有一个字典，各种方法遍历这个来执行各种任务。我的代码是单线程的，当尝试在第二次迭代中访问ArrayList中的下一个对象时，其中一个方法抛出ConcurrentModificationException。但是，我无法在迭代过程中找到任何实际更改ArrayList的内容。
import java.io.*;
import java.util.*;
public class Main {
private ArrayList<String> masterList;
private ArrayList<String> contains;
private ArrayList<String> doesNotContain;
private HashMap<Integer, ArrayList<String>> wordLengthList;
private HashMap<Integer, ArrayList<String>> difficultyList;
private int guesses = 10;
private Scanner sc;
private FileReader fr;
private BufferedReader br;
private String guessString;
private char guessChar;
private static final String DICTIONARY = "smalldictionary.txt";
private String wordLengthString;
private int wordLengthInt = 0;
public Main(){
masterList = new ArrayList<String>();
contains = new ArrayList<String>();
doesNotContain= new ArrayList<String>();
wordLengthList = new HashMap<Integer, ArrayList<String>>();
difficultyList = new HashMap<Integer, ArrayList<String>>();
sc = new Scanner(System.in);
importTestDictionary(); //does not use masterList
br = new BufferedReader(fr);
importWords(); //Adds to masterList. Both readers closed when finished.
catalogLengths(); //Iterates through masterList - does not change it.
do{
setWordLength(); //does not use masterList
}while(!(validateLengthInput(wordLengthString))); //validation will change the set of masterList if valid.
//Main loop of game:
while(guesses > 0){
do{
getUserInput();
}while(!(validateInput(guessString)));
splitFamilies();//will change set of masterList when larger group is found. Changes occur AFTER where Exception is thrown
printDifficultyList();
}
}
private void importWords(){ //Adds to masterList. Both readers closed when finished.
try{
while(br.readLine() != null){
line = br.readLine();
masterList.add(line);
}
br.close();
fr.close();
}catch(IOException e){
System.err.println("An unexpected IO exception occurred. Check permissions of file!");
}
}
private boolean validateLengthInput(String length){ //validation will change the set of masterList if valid.
try{
wordLengthInt = Integer.parseInt(length);
if(!(wordLengthList.containsKey(wordLengthInt))){
System.out.println("There are no words in the dictionary with this length.\n");
return false;
}
}catch(NumberFormatException e){
System.out.println("You must enter a number.\n");
return false;
}
masterList = wordLengthList.get(wordLengthInt);
return true;
}
private void splitFamilies(){ //will change set of masterList when larger group is found. Changes occur AFTER where Exception is thrown
Iterator<String> it = masterList.iterator();
int tempCount = 0;
while(it.hasNext()){
tempCount++;
System.out.println("tempCount: " + tempCount);
String i = it.next(); //Still throwing ConcurrentModification Exception
if(i.contains(guessString)){
contains.add(i);
}else{
doesNotContain.add(i);
}
}
if(contains.size() > doesNotContain.size()){
masterList = contains;
correctGuess(); //does not use masterList
profileWords();
}
else if(doesNotContain.size() > contains.size()){
masterList = doesNotContain;
incorrectGuess(); //does not use masterList
}
else{
masterList = doesNotContain;
incorrectGuess(); //does not use masterList
}
}
private void printMasterList(){ //iterates through masterList - does not change it.
for(String i : masterList){
System.out.println(i);
}
}
private void catalogLengths(){ //Iterates through masterList - does not change it.
for(String i : masterList){
if(i.length() != 0){
if(!(wordLengthList.containsKey(i.length()))){
wordLengthList.put(i.length(), new ArrayList<String>());
}
wordLengthList.get(i.length()).add(i);
}
}
}
}
抛出异常的行在代码中标记为上面。使用masterList的任何方法也都会被标记，包含任何不使用它的方法，都没有评论。
我确实阅读了一些答案，其中一些建议使用Iterator来避免异常。这在splitFamilies()上面实现。原始代码如下：
private void splitFamilies(){ //will change set of masterList when larger group is found. Changes occur AFTER where Exception is thrown
int tempCount = 0;
for(String i : masterList){ //This line throws ConcurrentModificationException
tempCount++;
System.out.println("tempCount: " + tempCount);
if(i.contains(guessString)){
contains.add(i);
}else{
doesNotContain.add(i);
}
}
....continue as before
tempCount始终为2。
也许我错过了一些非常简单的东西，但我已经尝试过跟踪这个，并且无法找出为什么我会得到这个例外！
我试图删除与代码无关的所有内容，但如果有人真的想查看完整的内容，我想我可以将所有代码转储到问题中！
答案 0 :(得分：2)
问题来自于masterList在第一次拆分后引用contains或doesNotContain这一事实。当您在masterList上进行迭代时，实际上您也会在另一个列表上同时进行迭代。
然后，您将项目添加到列表中：
if(i.contains(guessString)){
contains.add(i);
}else{
doesNotContain.add(i);
}
此处，您不仅要向contains或doesNotContain添加项目，还可以向masterList添加项目，这会导致conccurentException。
要解决您的问题，只需复制您的列表，而不是：masterList = contains;
使用以下代码复制：masterList = new ArrayList<>(contains);
同样适用于doesNotContains。
另一个想到的解决方案是为每个拆分重置两个列表contains和doesNotContains。由于您只在此方法中使用它们，而在其他任何地方使用它们，从您的类中删除这两个列表，并在splitFamilies