调用.next()后迭代器抛出IllegalStateException异常

Question

调用.next()后迭代器抛出IllegalStateException异常

javawhile-loopiteratorillegalstateexception

3

//This method compares two ArrayLists of strings and compares whether the words in one array list contain the letters in the other.

    public static void remove()
    {
        //Create iterators for both stringList and letterList
        Iterator<String> iterWords = stringList.iterator();
        Iterator<String> iterLetters = letterList.iterator();

        //First while loop will go over all strings in stringList via the iterWords iterator
        while(iterWords.hasNext())
        {
            //iterWords now has a .next() call

            String word = iterWords.next();
            //Second while loop that should run over each letter in letterList and compare it to each word in stringList
            while(iterLetters.hasNext())
            {
                //iterLetter now has a .next() call
                String letter = iterLetters.next();
                //if statement to remove the entry in stringList if it does not contain the current letter.  It is this part that throws the illegalstateexception
                if(word.contains(letter) == false)
                {
                    //This is the line that is causing the illegalstateexceptions
                    iterWords.remove();
                }           
            }
        }
    }

大家好，我正在寻求关于迭代两个ArrayList时遇到的异常的见解。我已经简化了上述的ArrayList并删除了与问题无关的任何方法。在最后一个iterWords.remove()上我得到了一个illegalstateexception异常。在外部while循环中，我已经执行了iterWords.next()，所以iterWords.remove()应该可以看到要删除的东西。
我猜想这是因为我从内部while循环中调用iterWords.remove()而引起的异常。你认为这可能是原因吗？感谢您能带来的任何见解。

- user2714543

嗯...一个用于“比较”事物的方法不应该被称为remove。 - Jim Garrison

是的，你说得很对。我只是为了发帖方便读者知道这就是出现.remove()问题的方法而给它起了这个名字。 - user2714543

1个回答

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- JB Nizet · Accepted Answer

首先，您应该阅读并发布异常信息。

其次：您在仅调用一次next()之后多次调用remove()：与单词中不包含的字母数量相同。

第三：由于您始终使用相同的字母迭代器，因此一旦完成第一个单词，您就不再迭代字母了。

因此，您必须：

stop iterating on letters as soon as you've removed the word
recreate the letter iterator at each iteration of the outer loop. Or better, just use a foreach loop: you don't need an iterator for the inner loop. Your code would be much simpler, readable and safer if you used methods:
```
for (Iterator<String> it: words; it.hasNext(); ) {
    String word : it.next();
    if (anyLetterNotInWord(letters, word) {
        it.remove();
    }
}
```

如果您使用的是Java 8，则可以将其简化为

words.removeIf(word -> anyLetterNotInWord(letters, word));

其中anyLetterNotInWord()可以被定义为

return letters.stream().anyMatch(letter -> !word.contains(letter));