Question

我是Java的新手，也是Scanner类的新手。我正在编写一个程序，要求用户输入一个单词，然后在一个文件中搜索这个单词。每次找到该单词时，它都会打印在JOptionPane中的新行以及它之前和之后的单词上。一切都按预期运作，但有两个例外：

如果搜索的单词恰好是文件中的最后一个单词，则会抛出“NoSuchElementException”。
如果被搜索的单词连续出现两次（不太可能，但我发现仍有问题），它只返回一次。例如，如果被搜索的单词是“had”和“他说他已经受够了。他已经整晚都在上面”是文件中的句子，那么输出是：
```
he had had
He had been
```
应该是：
```
he had had
had had enough.
He had been
```

我相信我的问题在于我使用了while(scan.hasNext())并且在此循环中我使用了scan.next()两次。我找不到解决方案，虽然仍然实现了我想要的程序返回。

这是我的代码：

//WordSearch.java
/*
 * Program which asks the user to enter a filename followed
 * by a word to search for within the file. The program then
 * returns every occurrence of this word as well as the
 * previous and next word it appear with. Each of these
 * occurrences are printed on a new line when displayed
 * to the user.
 */

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.util.ArrayList;
import java.util.Scanner;
import javax.swing.JOptionPane;

public class WordSearch {

    public static void main(String[] args) throws FileNotFoundException {

        String fileName = JOptionPane.showInputDialog("Enter the name of the file to be searched:");
        FileReader reader = new FileReader(fileName);

        String searchWord = JOptionPane.showInputDialog("Enter the word to be searched for in \"" + fileName + "\":");
        Scanner scan = new Scanner(reader);

        int occurrenceNum = 0;
        ArrayList<String> occurrenceList = new ArrayList<String>();
        String word = "", previousWord, nextWord = "", message = "", occurrence, allOccurrences = "";

        while(scan.hasNext()){
            previousWord = word;
            word = scan.next();

            if(word.equalsIgnoreCase(searchWord)){
                nextWord = scan.next();

                if(previousWord.equals("")){
                    message = word + " is the first word of the file.\nHere are the occurrences of it:\n\n";
                    occurrence = word + " " + nextWord;
                }
                else{
                    occurrence = previousWord + " " + word + " " + nextWord;
                }

                occurrenceNum++;
                occurrenceList.add(occurrence);
            }
        }

        for(int i = 0; i < occurrenceNum; i++){
            allOccurrences += occurrenceList.get(i) + "\n";
        }

        JOptionPane.showMessageDialog(null, message + allOccurrences);

        scan.close();
    }
}

此外，在旁注：我如何实施scan.useDelimeter()来忽略任何问号，逗号，句号，句点，撇号等？

Answer 1

如果搜索的单词恰好是文件中的最后一个单词，则会抛出NoSuchElementException。

这是因为这一行：

if(word.equalsIgnoreCase(searchWord)) {
    nextWord = scan.next();
    ...
}

您不会直接检查scan hasNext()是否scan.next()。您可以通过调用scan.hasNext()

添加条件来解决此问题

如果被搜索的单词连续出现两次（不太可能，但我发现仍有问题），它只会返回一次。

同样的问题在这里发挥作用：当你找到一个单词时，你立即检索下一个单词。

修复此问题有点棘手：您需要更改算法以一次查看一个单词，并使用previousWord（无论如何存储）以使用while的后续迭代循环。

Answer 2

你可以做的就是在再次使用next之前调用hasNext。

while(scan.hasNext()){
    previousWord = word;
    word = scan.next();

    if(word.equalsIgnoreCase(searchWord) && scan.hasNext()){ // this line change
        nextWord = scan.next();

        if(previousWord.equals("")){
            message = word + " is the first word of the file.\nHere are the occurrences of it:\n\n";
            occurrence = word + " " + nextWord;
        }
        else {
            occurrence = previousWord + " " + word + " " + nextWord;
        }

        occurrenceNum++;
        occurrenceList.add(occurrence);
    }
}

您希望不使用带有忽略大小写的等号。你想只使用.equals（）。

Answer 3

解决方案是以您当前保存previousWord的方式保存两个字词。类似的东西：

while (scan.hasNext()) {
    previousWord = word;
    word = nextWord;
    nextWord = scan.next();

然后你检查word。如果它符合您的需要，则可以与previousWord和nextWord一起打印。也就是说，在每次迭代中，您都在检查您在上一次迭代中读取的单词。

这样，您的循环中只需要一个hasNext()和一个next()。

请注意，在循环结束后，nextWord可能实际上是您的单词。这意味着你的单词是文件中的最后一个单词，你应该检查并相应地打印它。

扫描仪＆amp; .hasNext（）问题

3 个答案: