如何让文件阅读器没有异常？

Question

作业是读取文件的每个单词，并使用map统计每个单词出现的频率。然后使用给定的方法 sortByValue(Map map) 组织它们。我对如何让文件正确读取并将整数值分配给字符串键感到困惑。帮忙？

 import java.util.*;
 import java.io.*;
 public class WordFrequency {
     public static void main(String []args) throws IOException {

     File textFile = new File("book.txt"); 
     BufferedReader in = new BufferedReader(new FileReader(textFile));
     TreeMap<String, Integer> frequencyMap = new TreeMap<String, Integer>();
     String currentLine; 
     while ((currentLine = in.readLine()) != null) {
         currentLine = currentLine.toLowerCase();


     }

     StringTokenizer tokenizer = new StringTokenizer(currentLine, " \t\n\r\f.,;:!?'");

     while (tokenizer.hasMoreTokens()) { 
         final String currentWord = tokenizer.nextToken(); Integer frequency = frequencyMap.get(currentWord);
         if (frequency == null) { frequency = 0; } frequencyMap.put(currentWord,frequency + 1);

     }
     ArrayList map;
     map = sortByValue(frequencyMap);

     for(int i= 0; i < 20; i++)
         System.out.println(map.get(i));

     }

// Sort a map with its values in ascending order
public static ArrayList < Map . Entry > sortByValue ( Map map )
{
ArrayList < Map . Entry > a = new ArrayList ( map . entrySet () );
// sort by providing my own comparator
Collections . sort (a , new Comparator ()
{
public int compare ( Object o1 , Object o2 )
{
Map . Entry e1 = ( Map . Entry ) o1 ;
Map . Entry e2 = ( Map . Entry ) o2 ;
return (( Comparable ) e1 . getValue () ). compareTo ( e2 . getValue () ) ;
}
}) ;
return a;
}


 }

IOException 是

  Exception in thread "main" java.lang.NullPointerException
at java.util.StringTokenizer.<init>(Unknown Source)
at java.util.StringTokenizer.<init>(Unknown Source)
at WordFrequency.main(WordFrequency.java:20)

Answer 1

看看while ((currentLine = in.readLine()) != null) {

当这个循环退出时，currrentLine 将是null，这是循环的要求。

你应该考虑做的是在你用来读取文件的while循环中移动currentLine的处理......

例如...

while ((currentLine = in.readLine()) != null) {
     currentLine = currentLine.toLowerCase();
     StringTokenizer tokenizer = new StringTokenizer(currentLine, " \t\n\r\f.,;:!?'");

     while (tokenizer.hasMoreTokens()) { 
         final String currentWord = tokenizer.nextToken(); 
         Integer frequency = frequencyMap.get(currentWord);
         if (frequency == null) { 
             frequency = 0; 
         } 
         frequencyMap.put(currentWord,frequency + 1);
     }

 }

Answer 2

问题出在这里：

 while ((currentLine = in.readLine()) != null) {
     currentLine = currentLine.toLowerCase();
 }

您基本上只是浏览文件直到结束。然后将 null 保存在 currentLine 中，然后使用 null 调用 Tokenizer ---> NullPointerException。

添加一个新变量：

 String text = "";
 while ((currentLine = in.readLine()) != null) {
     text += currentLine.toLowerCase();
 }

然后将text 用于标记器。

Answer 3

在它变为空之前添加另一个字符串以获取currentLine，例如请参阅下面的entireText：

package org.fuzzyanalysis.demo;


import java.util.*;
import java.io.*;

public class WordFrequency {

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

         File textFile = new File("book.txt"); 
         BufferedReader in = new BufferedReader(new FileReader(textFile));
         TreeMap<String, Integer> frequencyMap = new TreeMap<String, Integer>();
         String currentLine; 
         String entireText = "";
         while ((currentLine = in.readLine()) != null) {

             currentLine = currentLine.toLowerCase();            
             entireText += currentLine;

         }

         StringTokenizer tokenizer = new StringTokenizer(entireText, " \t\n\r\f.,;:!?'");

         while (tokenizer.hasMoreTokens()) { 
             final String currentWord = tokenizer.nextToken(); Integer frequency = frequencyMap.get(currentWord);
             if (frequency == null) { frequency = 0; } frequencyMap.put(currentWord,frequency + 1);

         }
         ArrayList map;
         map = sortByValue(frequencyMap);

         for(int i= 0; i < 20; i++)
             System.out.println(map.get(i));

         }

    // Sort a map with its values in ascending order
    public static ArrayList < Map . Entry > sortByValue ( Map map )
    {
        ArrayList < Map . Entry > a = new ArrayList ( map . entrySet () );
        // sort by providing my own comparator
        Collections . sort (a , new Comparator ()
        {
            public int compare ( Object o1 , Object o2 )
            {
                Map . Entry e1 = ( Map . Entry ) o1 ;
                Map . Entry e2 = ( Map . Entry ) o2 ;
                return (( Comparable ) e1 . getValue () ). compareTo ( e2 . getValue () ) ;
            }
        }) ;
    return a;
    }


}