java - 无法弄清楚是什么触发了 "java.util.ConcurrentModificationException"

Question

我的代码抛出了一个我以前从未见过的错误。所以嘿!我想我正在学习；)无论如何，我做了一些阅读，通常当正在迭代的列表在迭代中被修改时会抛出此错误。不过，我很确定我不会修改它。当在partition()上抛出错误时，如果我没有在updateCurrentList()中为currentList分配新值(通过注释掉代码)，程序将不再抛出错误。在我的 play() 方法中，这两个函数被依次调用，但是列表迭代应该在进行更改时完成。我缺少什么？我是否必须以某种方式关闭迭代器？

package hangman;
import java.io.*;
import java.util.*;
import javax.swing.JOptionPane;

public class Hangman {
    private Map<String, List<String>> wordPartitions; // groups words according to positions of guessed letter
    private List<String> currentList; // remaining possible words that fit the information given so far
    Set<Character> wrongGuesses; // holds all the "wrong" guesses so far
    StringBuilder guessString; // current state of the word being guessed
    String justHyphens; // for checking whether a guess was "wrong"

    // initialize fields
    // currentList should contain all (and only) words of length wordLength

// justHyphens and guessString should consist of wordLength hyphens
public Hangman(int wordLength) throws FileNotFoundException {
    this.currentList = new ArrayList<String>();
    addWords(wordLength);
    wrongGuesses = new HashSet();

    for(int i = 0; i < wordLength; i++) {
        justHyphens += "-";
    }
    guessString = new StringBuilder();
    wordPartitions = new HashMap();
}

private void addWords(int wordLength) throws FileNotFoundException {
    Scanner words = new Scanner(new File("lexicon.txt"));
    String word = "";

    while(words.hasNext()) {
        word = words.next();
        if (word.length() == wordLength) {
            currentList.add(word);
        }
    }
}

// main loop
public void play() {
    char choice;

    do {
        choice = getUserChoice();
        partition(choice);
        updateCurrentList(choice);
    } while (!gameOver());
        endMessage();
}

// display the guessString and the missed guesses
// and get the next guess
private char getUserChoice() {
   //generate a string from the incorrect choices char list
    String wrong = "";
    char letter;

    if(!wrongGuesses.isEmpty()) {
        Iterator<Character> letters = wrongGuesses.iterator();
        letter = letters.next(); 

        while(letters.hasNext()) {
            letter = letters.next();
            wrong += ", " + letter;
        }
    }

    String letterStr = JOptionPane.showInputDialog("Incorrect choices: "+ wrong +"\n Tested letters: "+ guessString.toString() +"\nplease input a letter.");
    return letterStr.charAt(0);
}


// use wordPartitions to partition currentList using
// keys returned by getPartitionKey()
private void partition(char choice) {

    String word = "";
    String key = "";
    List<String> tempList = new ArrayList<String>();

    Iterator<String> words = currentList.iterator();
    //Generate a key for each word and add to appropriate arraylist within map.
    while(words.hasNext()) {
        word = words.next();
        key = getPartitionKey(word, choice);

        if(wordPartitions.containsKey(key)) {
            tempList = wordPartitions.get(key);
            tempList.add(word);
            wordPartitions.put(key, tempList);
        } else {
            tempList.clear();
            tempList.add(word);
            wordPartitions.put(key, new ArrayList<String>());                
        }            
    }
}

// update currentList to be a copy of the longest partition
// if choice was "wrong", add choice to wrongGuesses
// if choice was "right", update guessString
private void updateCurrentList(char choice) {        
    String key = findLongestList();

    currentList = wordPartitions.get(key);

    if(key.equals(justHyphens)) {
        wrongGuesses.add(choice);
    } else {
        addLetterToGuessString(guessString, choice, key);
    }
}

private String findLongestList() {
    Set<String> keySet = wordPartitions.keySet();
    Iterator<String> keys = keySet.iterator();
    String maxKey = "";
    int maxKeyLength = 0;
    List<String> tempList;
    String tempKey = "";

    while(keys.hasNext()) {
        tempKey = keys.next();
        tempList = wordPartitions.get(tempKey);

        if(tempList.size() > maxKeyLength) {
            maxKeyLength = tempList.size();
            maxKey = tempKey;
        }
    }

    return maxKey;
}

// checks for end of game
private boolean gameOver() {
    return false;
}

// display the guessString and the missed guesses
// and print "Congratulations!"
private void endMessage() {
    JOptionPane.showMessageDialog(null, "Congrats, yo!");
}

// returns string with '-' in place of each
// letter that is NOT the guessed letter
private String getPartitionKey(String s, char c) {
    String word = "";
    String letter = Character.toString(c);
    for(int i = 0; i < s.length(); i++) {
        if(s.charAt(i) == c) {
            word += letter;
        } else {
            word += "-";
        }
    }

    return word;
}
// update guessString with the guessed letter
private void addLetterToGuessString(StringBuilder guessString, char letter, String key) {
    for(int i = 0; i < key.length(); i++) {
        if(key.charAt(i) != '-') {
            guessString.setCharAt(i, key.charAt(i)); 
        } 
    }
}

}

Answer 1

问题在于您在迭代集合时正在修改集合。

集合是currentList，您正在partition()中迭代它。当您向此处的 tempList 添加单词时，您可以修改它:

key = getPartitionKey(word, choice);

if(wordPartitions.containsKey(key)) {
    tempList = wordPartitions.get(key);
    tempList.add(word);
    wordPartitions.put(key, tempList);
} else {

为什么？因为之前您从 play() 调用了 updateCurrentList():

do {
    choice = getUserChoice();
    partition(choice);
    updateCurrentList(choice);
} while (!gameOver());

并且您更新了 currentList:

String key = findLongestList();

currentList = wordPartitions.get(key);

因此，如果 getPartitionKey(word, choice) 返回的 key 与之前由 findLongestList() 返回的键相同， currentList 将与 tempList 相同，因此您将修改正在迭代的集合。

解决方案？如果 tempList 与 currentList 相同，则不要向其中添加该单词(根据定义，它已经具有该单词)。所以，你可以像这样重写你的 if-else (我删除了一些无用的代码):

if(wordPartitions.containsKey(key)) {
    tempList = wordPartitions.get(key);
} else {
    wordPartitions.put(key, new ArrayList<String>());                
}

if (tempList!=currentList) {
    tempList.add(word);
}