java – 为什么我抛出NullPointerException

所以这对大学来说是一个寒假,而我正试图在编码上保持敏锐,所以我只是编写程序和算法的代码,我们只讨论但从未在课堂上编码.无论如何,我今天正在研究的是一个程序,你给计算机一个扰乱的单词,它输出所有可以从这些字母中产生的单词(来自我们给出的EnglishWordList文件).

无论如何,这是我到目前为止的代码：

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

public class ProdFinder {
    private HashMap<Character,Integer> prodFinder = new HashMap<Character,Integer>();
    private HashMap<Integer,LinkedList<String>> findWord = new HashMap<Integer,LinkedList<String>>();

    private static final char[] letters =     {'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z'};
    private static final int[] primes =     {2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97,101}; 

    public ProdFinder() throws FileNotFoundException {
        for (int i = 0; i < letters.length; i++) {
            prodFinder.put(letters[i],primes[i]);
        }

        Scanner sc = new Scanner(new File("EnglishWordList.txt"));


        while (sc.hasNextLine()) {
            String str = sc.nextLine();
            int strProd = findProduct(str);

            if (findWord.containsKey(strProd)) {
                LinkedList<String> wordList = findWord.get(strProd);
                wordList.add(str);
                findWord.put(strProd,wordList);
            }
            else {
            LinkedList<String> wordList = new LinkedList<String>();
            wordList.add(str);
            findWord.put(strProd,wordList);
        }
    }

    sc.close();
}

public int findProduct(String x) {
    int product = 1;
    char[] str = x.tochararray();

    for (Character val: str) {
        product = product*prodFinder.get(val);
    }

    return product;
}

public void descramble(String x) {
    int prod = findProduct(x);

    if (findWord.containsKey(prod)) {
        System.out.println("The words that can be formed from the letters in " + x + " are: " +
                            findWord.get(prod));
    }
    else {
        System.out.println("No words can be formed from the letters in " + x + ".");
    }
}

}

现在,错误起源于我开始将数字的所有主要产品放入我的HashMap的行(试图将每个主要产品映射到其字母乘以该数字的单词的LinkedList.)不知何故,这是抛出异常,如当我注释掉那部分代码并运行findProduct方法时,它可以正常工作,我将它输出为以黄金形式输出lettesr的产品.

有关异常来自何处的任何想法？

编辑：抱歉,堆栈跟踪如下：

Exception in thread "main" java.lang.NullPointerException
at ProdFinder.findProduct(ProdFinder.java:44)
at ProdFinder.<init>(ProdFinder.java:22)
at Descramble.main(Descramble.java:7)

据我所知,当我尝试在str上调用findProd时,错误就出现了：

int strProd = findProduct(str);

product = product*prodFinder.get(val);