程序运行：从文件中获取单词给它们一个哈希值，如果发生冲突则将它们放入数组中在数组中创建一个列表。
当我打印一个相互冲突的列表时，我可以将它们插入并半打印正确，它只打印最后插入的列表。问题是当我打印整个数组时，我得到了一个空指针异常停止。
这是我从链表移动到链表的代码，以及我收到错误的地方：
Exception in thread "main" java.lang.NullPointerException
at p7b.main(p7b.java:45)
错误：
class WordList{
public Word firstWord = null;
public void insert(Word newWord, int hashKey){
Word prev = null;
Word curr = firstWord;
newWord.key = hashKey;
while(curr != null && newWord.key > curr.key){
prev = curr;
curr = curr.next;
}
if(prev == null)
firstWord = newWord;
else
prev.next = newWord;
newWord.next = curr;
}//end insert
public String display(){
if(firstWord == null){
return "null";
}
Word curr = firstWord;
while (curr != null){
System.out.println(curr.returnWord() + " " +curr.returnHashVal());
curr = curr.next;
}
return "done";
}//end display
我不明白为什么我会继续这样做。
完整代码：
WordList类 https://www.dropbox.com/s/6a4pk7kt2cllgga/WordList.java?dl=0
import java.util.*;
class Word{
protected String theWord;
protected int hashValue;
protected Word next;
protected int key;
public Word(String theWord,int hashValue){
this.theWord = theWord;
this.hashValue = hashValue;
}
public String returnWord(){
return theWord;
}
public int returnHashVal(){
return hashValue;
}
}//end class
词类 https://www.dropbox.com/s/hzrksrdwhbiw6on/Word.java?dl=0
import java.util.*;
import java.io.*;
public class p7b{
public static void main(String[] args){
int[] arrayNums = new int[40];
Object[] arrayString = new Object[40];
// Location of file to read
File file = new File("p7.dat");
try {
Scanner in = new Scanner(file);
while (in.hasNextLine()) {
String key = in.nextLine(); //READ LINE
System.out.println("Input: "+key); //PRNT LINE
int length = length(key); //KEY LENGTH
//System.out.println(length); //PRNT LENGTH
int Val = assignVal(0,key);
//System.out.println("val: "+Val);
int ValTwo = assignVal(length-1,key);
//System.out.println("valTwo: "+ValTwo);
int hashVal = keyVal(Val,ValTwo);
//System.out.println("hash value: " + hashVal);
Insert(hashVal,key,arrayNums,arrayString);
//arrayNums[hashVal] = hashVal;
//arrayString[hashVal] = key;
}
for(int i = 2; i < 38; i++){
//System.out.println(arrayString[i]+" "+arrayNums[i]);
//System.out.println(String.format("Word:%11s-----------Hash Value:%5s ".replace(" ", "ƒ"),
// arrayString[i], arrayNums[i]).replace(" ", "-").replace("ƒ", " "));
WordList list = (WordList)arrayString[i];
list.display();
}
in.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
}
}//end main
//-------------------------------------------------------------
public static void Insert(int hashVal, String key,int[] arrayNums, Object[] arrayString){
Word word = new Word(key,hashVal);
WordList list = new WordList();
arrayString[hashVal] = list;
//System.out.println("here");
list.insert(word,hashVal);
//System.out.println("X");
//list.display();
}//end Insert
public static int keyVal(int first,int last){
int num = first + last;
return num;
}//end keyVal
public static int length(String key){
int length = key.length();
return length;
}//end length
public static int assignVal(int position, String key){
char Hkey = key.charAt(position);
int Val = 0;
switch(Hkey) {
case 'A': Val = 11;
break;
case 'B': Val = 15;
break;
case 'C': Val = 1;
break;
case 'D': Val = 0;
break;
case 'E': Val = 0;
break;
case 'F': Val = 15;
break;
case 'G': Val = 3;
break;
case 'H': Val = 15;
break;
case 'I': Val = 13;
break;
case 'J': Val = 0;
break;
case 'K': Val = 0;
break;
case 'L': Val = 15;
break;
case 'M': Val = 15;
break;
case 'N': Val = 13;
break;
case 'O': Val = 0;
break;
case 'P': Val = 15;
break;
case 'Q': Val = 0;
break;
case 'R': Val = 14;
break;
case 'S': Val = 6;
break;
case 'T': Val = 6;
break;
case 'U': Val = 14;
break;
case 'V': Val = 10;
break;
case 'W': Val = 6;
break;
case 'X': Val = 0;
break;
case 'Y': Val = 13;
break;
case 'Z': Val = 0;
break;
}//end switch
return Val;
}//end assignVal
}//end class
主 https://www.dropbox.com/s/3o46bp1i3aqanih/p7b.java?dl=0
Access to an object's fields is only permitted within its methods.
- 非常感谢帮助。