無法找出引發“ java.util.ConcurrentModificationException”的原因

Question

我的代碼拋出了一個我從未見過的錯誤。 嘿！ 我想我正在學習;）無論如何，我做了一些閱讀，並且通常在迭代過程中修改一個迭代列表時會拋出此錯誤。 但是，我很確定我沒有對其進行修改。 當錯誤被拋出在partition（）上時，如果我沒有在updateCurrentList（）中為currentList分配新值（通過注釋掉代碼），則程序不再拋出錯誤。 這兩個函數在我的play（）方法中一個接一個地調用，但是列表迭代應該在進行更改時完成。 我想念什么？ 我是否必須以某種方式關閉迭代器？

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

問題是您在迭代一個集合時正在修改它。

該集合是currentList ，您正在partition()對其進行迭代。 當您在此處向tempList添加單詞時，可以tempList修改：

key = getPartitionKey(word, choice);

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

為什么呢 因為以前您是從play()調用updateCurrentList() play() ：

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

然后您更新了currentList ：

String key = findLongestList();

currentList = wordPartitions.get(key);

因此，如果key由歸國getPartitionKey(word, choice)是與先前通過返回鍵findLongestList() currentList將是相同的tempList ，所以你會修改你迭代的集合。

解決方案 ？ 如果tempList與currentList相同，則不要在其中添加單詞（根據定義，該單詞已經包含該單詞）。 因此，您可以像這樣重寫if-else（我刪除了一些無用的代碼）：

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

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