java – Scanner&.hasNext()问题

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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,则抛出“NoSuchElementException”.
>如果被搜索的单词连续出现两次(不太可能,但仍然是我发现的问题),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.他整晚都在上面”是文件中的句子,那么输出是：

he had had
He had been

而它应该是：

he had had
had had enough.
He had been

我相信我的问题在于我使用了一段时间(scan.hasNext())并且在这个循环中我使用了scan.next()两次.虽然我找不到解决方案,但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：我如何实现scan.useDelimeter()来忽略任何,问号,逗号,句号,撇号等？

解决方法:

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();
    ...
}

您不检查扫描是否实际上是hasNext(),直接扫描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.

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循环的后续迭代.

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