NullPointerExcetion本机方法访问器...散列字问题 [英] NullPointerExcetion Native Method Accessor... Hashing Words Issue

问题描述

我正在写一个读取文件并对单词进行排序的项目。这段代码编译正确，然后它给了我一个空指针异常。任何想法？

  import java.io.File; 
 import java.io.FileNotFoundException; 
 import java.util.Scanner; 
 import java.util.Hashtable; 
 
 public class Lab {
 Hashtable< String，Word> words = new Hashtable< String，Word>（）; 
 
 public void addWord（String s，int i）{
 if（words.containsKey（s））{
 words.get（s）.addOne（）; 
 words.get（s）.addLine（i）; 
} else {
 words.put（s，new Word（s））; 
 words.get（s）.addLine（i）; 
 
 
 
 public void main（String [] args）{
 System.out.println（HI）; 
档案档案=新档案（s.txt）; 
 int linecount = 1; 
尝试{
扫描仪扫描仪=新的扫描仪（文件）; 
 System.out.println（HUH）; 
 
 while（scanner.hasNextLine（））{
 String line = scanner.nextLine（）; 
 while（line！= null）{
 String word = scanner.next（）; 
 addWord（word，linecount）; 
} 
 linecount ++; 
 $ b} 
} catch（FileNotFoundException e）{
 e.printStackTrace（）; 
 
 
 
 
 
 
异常的堆栈跟踪是：
  java.lang.NullPointerException $ b $在sun.reflect.NativeMethodAccessorImpl.invoke0（本地方法）
在太阳.reflect.NativeMethodAccessorImpl.invoke（Unknown Source）
 at sun.reflect.DelegatingMethodAccessorImpl.invoke（Unknown Source）
 at java.lang.reflect.Method.invoke（Unknown Source）
 at edu .rice.cs.drjava.model.compiler.JavacCompiler.runCommand（JavacCompiler.java:27 1）
  
 
 
 while while  loop is strange：
  code> while（scanner.hasNextLine（））{
 String line = scanner.nextLine（）; 
 while（line！= null）{
 String word = scanner.next（）; 
 addWord（word，linecount）; 
} 
 linecount ++; 
 
 $ / code> 
如果您的输入文件是： 
 
 
  a 
b 
  
然后 scanner.nextLine（）会返回 a ，然后 scanner.next（） nextLine 返回下一行以分隔符结束的字符串，并且<$ c $>会返回 b  c> next 从输入文件返回下一个标记。这真的是你想要的吗？我建议试试这个： 
 
 
  while（scanner.hasNextLine（））{{
 String word = scanner。 nextLine（）; 
 addWord（word，linecount）; 
 
 linecount ++; 
} 
  
请记住，这只适用于每行只有一个字的情况。如果你想处理每行多个单词，它会稍微长一点：
  while（scanner.hasNextLine（））{ {
 String line = scanner.nextLine（）; 
 
扫描仪lineScanner =新扫描仪（线）; 
 while（lineScanner.hasNext（））{
 addWord（lineScanner.next（），linecount）; 
} 
 
 linecount ++; 
} 
  
 
I am writing a project that reads a file and sorts "Words". This code compiles correctly, yet then it gives me a null pointer exception. Any Ideas?
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
import java.util.Hashtable;

public class Lab {
   Hashtable<String, Word> words = new Hashtable<String, Word>();

   public void addWord(String s, int i) {
      if (words.containsKey(s)) {
         words.get(s).addOne();
         words.get(s).addLine(i);
      } else {
         words.put(s, new Word(s));
         words.get(s).addLine(i);
      }
   }

   public void main(String[] args) {
      System.out.println("HI");
      File file = new File("s.txt");
      int linecount = 1;
      try {
         Scanner scanner = new Scanner(file);
         System.out.println("HUH");

         while (scanner.hasNextLine()) {
            String line = scanner.nextLine();
            while (line != null) {
               String word = scanner.next();
               addWord(word, linecount);
            }
            linecount++;

         }
      } catch (FileNotFoundException e) {
         e.printStackTrace();
      }
   }
}
The exception's stacktrace is:
java.lang.NullPointerException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at edu.rice.cs.drjava.model.compiler.JavacCompiler.runCommand(JavacCompiler.java:27‌​1)

解决方案
This whileloop is strange:
while (scanner.hasNextLine()) {
    String line = scanner.nextLine();
    while (line != null) {
       String word = scanner.next();
       addWord(word, linecount);
    }
    linecount++;
}
If your input file is:
a
b
Then scanner.nextLine() would be return a, then scanner.next() would return b, because nextLine returns the next end-line delimited String, and next returns the next token from the input file. Is this really what you want? I'd suggest trying this:
while (scanner.hasNextLine()) {{
    String word = scanner.nextLine();
    addWord(word, linecount);

    linecount++;
}
Keep in mind that this would only work if there's only a word per line. If you want to handle multiple words per line, it'd be slightly longer:
while (scanner.hasNextLine()) {{
    String line = scanner.nextLine();

    Scanner lineScanner = new Scanner(line);
    while(lineScanner.hasNext()) {
        addWord(lineScanner.next(), linecount);
    }

    linecount++;
}


                        
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