java - 扫描仪和 .hasNext() 问题

Question

我是 Java 的新手，也是 Scanner 类的新手。我正在编写一个程序，它要求用户输入一个词，然后在一个文件中搜索这个词。每次找到该单词时，它都会打印在 JOptionPane 中的新行上，以及它前后的单词。一切正常，但有两个异常(exception):

1. 如果要搜索的词恰好是文件中的最后一个词，则会抛出“NoSuchElementException”。

2. 如果正在搜索的词连续出现两次(不太可能，但仍然是我发现的问题)，它只会返回一次。例如，如果要搜索的词是“had”，“He said that he had had had had had enough. He had been up all night”是文件中的句子，则输出为:

   he had had
   He had been
   

   而它应该是:

   he had had
   had had enough.
   He had been
   

我认为我的问题在于我使用了 while(scan.hasNext()) 并且在这个循环中我使用了两次 scan.next() .虽然我找不到解决方案，但仍能实现我希望程序返回的结果。

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，附带说明:我如何实现 scan.useDelimeter() 以忽略任何问号、逗号、句号、撇号等？

Answer 1

If the word being searched for happens to be the last word in the file then a NoSuchElementException is thrown.

这是因为这一行:

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

你不检查 scan实际上hasNext() , 直奔 scan.next() .您可以通过调用 scan.hasNext() 添加条件来解决此问题

If the word being searched for appears twice in a row (unlikely, but still a problem I discovered), it only returns it once.

这里也存在同样的问题:当您找到一个词时，您会立即检索下一个词。

解决这个问题有点棘手:您需要将算法更改为一次查看一个单词，并使用 previousWord (无论如何你都存储)用于 while 的后续迭代循环。