我在代码中的几个不同的地方收到一个nullpointer异常。我确信我已经忘记了一个例外，但我需要一些帮助来指出它。我有3个文件可以与整个程序一起使用。我正在根据给出的主文件创建一个anagramManager。
这是第一堂课
import java.util.*;
public class Word implements Comparable<Word>
{
private String word;
private String canonical;
public Word(String word)
{
String lowerCase = word.toLowerCase();
word = lowerCase;
canonical = CanonicalForm(word);
}
public String getWord()
{
return word;
}
public String getForm()
{
return canonical;
}
public String toString()
{
return "[" + word + "=" + canonical + "]";
}
public int compareTo(Word someWord)
{
return getForm().compareTo(someWord.getForm());
}
private static String CanonicalForm(String word)
{
if(word == null || word.length() < 1)
{
throw new IllegalArgumentException();
}
char arr[] = word.toCharArray();
Arrays.sort(arr);
return new String(arr);
}
}
这是anagramManager，它处理主文件夹上的大部分工作。
import java.util.*;
public class AnagramManager
{
private Word[] words;
private Random rand;
private Map<String,Set<String>> theMap;
public AnagramManager(List<String> list)
{
if (list == null || list.size() < 1)
{
throw new IllegalArgumentException();
}
rand = new Random();
words = new Word[list.size()];
theMap = new TreeMap<String,Set<String>>();
makeWords(list);
makeAnagrams();
}
public void sortByWord()
{
for (Word i : words)
{
i.getWord();
}
Arrays.sort(words);
}
public void sortByForm()
{
for(Word c : words)
{
c.getForm();
}
Arrays.sort(words);
}
public String getAnagram(String word)
{
String canonWord = CanonicalForm(word);
if(theMap.containsKey(canonWord))
{
Set<String> anagramSet = theMap.get(canonWord);
String[] match = anagramSet.toArray(new String[anagramSet.size()]);
return match[rand.nextInt(match.length)];
}
else
{
return "";
}
}
public Set<String> getAnagrams(String word)
{
String canonWord = CanonicalForm(word);
boolean hasAnagram = theMap.containsKey(canonWord);
Set<String> anagrams = (hasAnagram) ? theMap.get(canonWord) : new TreeSet<String>();
return anagrams;
}
public String toString()
{
String printWords = "";
int length = words.length;
if (length < 1)
{
printWords += "[]";
}
else
{
for (int i=0; i < length; i++)
{
printWords += words[i];
}
printWords += "[...]";
for(int i = length - 5; i < length; i++)
{
printWords += words[i];
}
}
return printWords;
}
private static String CanonicalForm(String word)
{
if(word == null || word.length() < 1)
{
throw new IllegalArgumentException();
}
char arr[] = word.toCharArray();
Arrays.sort(arr);
return new String(arr);
}
private void makeWords(List<String> list)
{
int ind = 0;
for (String orgWord : list)
{
words[ind] = new Word(orgWord);
ind++;
}
}
private void makeAnagrams()
{
for(Word i : words)
{
String canon = i.getForm();
String org = i.getWord();
if(!theMap.containsKey(canon))
{
Set<String> set = new TreeSet<String>();
set.add(org);
theMap.put(canon,set);
}
else
{
theMap.get(canon).add(org);
}
}
}
}
这是主程序。这根本不应该修改。
import java.util.*;
import java.io.*;
public class AnagramMain {
public static final String DICTIONARY_FILE = "dictionary.txt";
public static void main(String[] args) throws FileNotFoundException {
System.out.println("Welcome to the CS145 Anagram Practice");
System.out.println();
// open the dictionary file and read dictionary into an ArrayList
Scanner input = new Scanner(new File(DICTIONARY_FILE));
Scanner keyboard = new Scanner(System.in);
List<String> dictionary = new ArrayList<String>();
while (input.hasNext()) {
dictionary.add(input.next().toLowerCase());
}
// set up the AnagramManager
List<String> dictionary2 = Collections.unmodifiableList(dictionary);
AnagramManager catalog = new AnagramManager(dictionary2);
// Start the program asking for run style
System.out.println("Press enter to start, or any other input for debug mode");
String DEBUG = keyboard.nextLine();
// If in DEBUG mode
if (!DEBUG.equals("") )
{
System.out.println("** The first and last five sorted by word elements are **");
catalog.sortByWord();
System.out.println(catalog);
System.out.println("** The first and last five sorted by form elements are **");
catalog.sortByForm();
System.out.println(catalog);
System.out.println("\n\n\n");
}
// Start the Loop
getAnagram(keyboard, catalog);
}
// Executes the primary anagram loop
public static void getAnagram(Scanner console, AnagramManager theCatalog)
{
String input;
System.out.println("Please type in a word to anagram or QUIT to quit :");
input = console.nextLine();
while (!input.toUpperCase().equals("QUIT") && !input.equals("") )
{
String result = theCatalog.getAnagram(input);
if (!result.equals("") )
{
System.out.print("One possible anagram of your word " + input );
System.out.println(" is " +result);
}
else
{
System.out.println("Your word was not found in the list");
}
System.out.print("In fact the list of anagrams for your word are : ");
System.out.println(theCatalog.getAnagrams(input));
System.out.println("Please type in a word to anagram or QUIT to quit :");
input = console.nextLine();
}
}
}
例外情况如下：
Exception in thread "main" java.lang.NullPointerException
at java.util.TreeMap.compare(TreeMap.java:1294)
at java.util.TreeMap.put(TreeMap.java:538)
at java.util.TreeSet.add(TreeSet.java:255)
at AnagramManager.makeAnagrams(AnagramManager.java:129)
at AnagramManager.<init>(AnagramManager.java:21)
at AnagramMain.main(AnagramMain.java:28)
答案 0 :(得分：0)
您在Word的构造函数中遇到错误：
public Word（String word） { String lowerCase = word.toLowerCase（）; word = lowerCase; canonical = CanonicalForm（word）; }
您将新下限值重新分配给参数 word的第二行，但我怀疑您想将其分配给具有相同名称的字段，请更改对此：
this.word = lowerCase;