java.lang.NullPointerException,不知道为什么？

Question

我正在编写一个程序,它将一系列单词分成标记并读取文本,然后计算它们的频率.此代码有几个相关代码(WordCount,FreqStudy和Echo),但WordFreq类是导致java.lang.NullPointerException错误的原因.这是我的WordFreq代码:

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

public class WordFreq extends Echo{

  WordCount[] wcArray;
  int ct;
  String[] sentence;
  double freq;
  String newLine;

  public WordFreq(String f, String words) throws IOException{
    super(f);
    String[] wordString = words.split(" ");
    for(int i=0; i<wordString.length; i++)
      wcArray[i] = new WordCount(wordString[i]);
    Scanner scan = new Scanner(new FileReader(fileName));
  }

  public void processLine(String line){
    newLine = line.toLowerCase();
    sentence = newLine.split(" "); 
    for(String s: sentence){
      for(WordCount w: wcArray){
        if(w.getWord().equals(s))
          w.incCount();
      }
      ct++;
    }     
  }

  public void reportFrequencies(){
    for (int i=0; i<wcArray.length; i++){
      freq = (wcArray[i].getCount() / ct); 
      System.out.print(wcArray[i].getWord()+" ");
      System.out.printf("%6.4f\n", freq);
    }
  }
}

当我给它一个文件来读取FreqStudy主类时,我收到的错误看起来像这样:

java.lang.NullPointerException
    at WordFreq.<init>(WordFreq.java:17)
    at FreqStudy.main(FreqStudy.java:14)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at edu.rice.cs.drjava.model.compiler.JavacCompiler.runCommand(JavacCompiler.java:272)

我真的不明白这个问题是什么,我整天都在努力,所以我觉得脑子已经死了.如果可以,请看看,我真的很感激.

编辑:我意识到我没有在发布后立即初始化它,但我的频率返回0结果.有人帮吗？

Answer 1

wcArray在分配任何值之前初始化数组:

wcArray = new WordCount[wordString.length];