Java内部类迭代器问题

Question

我在使用内部 Iterator 时遇到困难。

private List<List<? extends HasWord>> sentences = new ArrayList<List<? extends HasWord>>(); 
private Iterator<String> wordIterator = new Words();
private class Words implements Iterator<String> {

    int currSentence = 0;
    int currWord = 0;

    @Override
    public boolean hasNext() {
        return currSentence != sentences.size() - 1 && currWord != sentences.get(currSentence).size() - 1;
    }

    @Override
    public String next() {
        String nextWord = sentences.get(currSentence).get(currWord).word();
        currSentence++;
        currWord++;

        return nextWord;
    }

    @Override
    public void remove() {
        throw new UnsupportedOperationException();          
    }

}

然后，我尝试遍历它:

for (String s : wordIterator) { //Error: Can only iterate over an array or an instance of java.lang.Iterable
            words.add(s);

但它不起作用。 (请参阅有问题的行上注释的编译器错误)。我在这里做错了什么？

根据工程说明，解决我的问题的正确方法是什么？我有一堆这种形式的循环:

    for (List<? extends HasWord> sent : sentences) {
        for (HasWord token : sent) {
            //do stuff
        }
        }

所以我决定 Iterator 会更简洁。这是矫枉过正，还是有其他方法可以做到？

Answer 1

有两个嵌套的 for 从根本上没有错循环执行此操作，但我认为这会更干净:

public class Words implements Iterator<String> {
  private final Iterator<HasWord> sentences;
  private Iterator<String> currentSentence;

  public boolean hasNext() {
    return currentSentence.hasNext() || sentences.hasNext();
  }

  public String next() {
    if (currentSentence.hasNext()) {
      return currentSentence.next();
    }
    currentSentence = sentences.next();
    return next(); // will return the first word of the next sentence
  }
  //remove() omitted for brevity
}

每当你需要一个遍历几个句子的迭代器时，返回这个类的一个新实例，并初始化 sentences字段使用 sentences.iterator();

(更仔细阅读您的问题后编辑)