Quadratic probing not working in insert function, HELP!!

Question

I have code that reads in a file of words and inserts them into a index of the array based on their hash value. Now some words have the same hash value, such as "truck" and "lo" which are both in the file i have. The file is in alphabetical order, so it should put truck in table[11889] and when it gets to lo, the insert method should see that it is not null and it should quadratically put this in a null location, but its overwriting truck, so when i search for truck, it does not find it.
Here is the code:
import java.io.*;
public class HashTable {
private String[] table = new String[59999];
private int numentries;
static int i = 1;
static int j = 1;
public HashTable()
public int hashFunction(String w)
int slot = 1;
for(int i = 0; i < w.length();i++)
slot *= (int)w.charAt(i);
slot = slot%59999;
if(slot < 0)
slot +=59999;
return slot;
public boolean search(String w)
int value;
value = hashFunction(w);
if(value < 0)
value+= 59999;
if(table[value].equals(w))
return true;
else
while(value < 59999)
if(table[value].equals(w))
return true;     
value = (value + j * j)%59999;
if(value < 0)
value+= 59999;
j++;
return false;
public void insert(String w)
int value;
value = hashFunction(w);
if(value < 0)
value+= 59999;
if(table[value] == null)
table[value] = w;
else
while(table[value]!= null)
value = (value + i * i)%59999;
if(value < 0)
value+= 59999;
i++;
table[value] = w;
public static void main(String[] args) throws IOException
HashTable hashTable = new HashTable();
String word;
String file;
String check;
System.out.println("Welcome to the SpellChecker!");
System.out.println("Enter the name of your dictionary file.");
BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
//file = input.readLine();
FileReader fr1 = new FileReader("c:\\general\\words.txt");
BufferedReader keyboard = new BufferedReader(fr1);
while((word = keyboard.readLine())!=null)
hashTable.insert(word);
keyboard.close();
System.out.println("Great, you dictionary has been stored in memory.");
System.out.println("What word would you like to check");
word = input.readLine();
if(hashTable.search(word))
System.out.println(word + " is a valid word in the dictionary");
else
System.out.println(word + " is not a valid word");
System.out.println("Would you like to check another word?");
check = input.readLine();
while(check.equals("yes"))
System.out.println("What word would you like to check?");
word = input.readLine();
if(hashTable.search(word))
System.out.println(word + " is a valid word in the dictionary");
else
System.out.println(word + " is not a valid word");
System.out.println("Would you like to check another word?");
check = input.readLine();
System.out.println("Thank you for using the SpellChecker!");
}

Answer 1

ok, i'm extremely new to java programming. I want to know more about hashtables and i've found that this was the best example i've found so far. Unfortunately there's no comments, in it, so i don't know what is going on in some places. For example, what is the method that is used to put the words into the table? how can you change it? Is there a special way that the words have to be put into the txt file? does it count periods and commas as a null space or does it count them as a character? aslo, when i run the program, i get the following runtime error:
Exception in thread "main" java.lang.NullPointerException
at HashTable.search(HashTable.java:45)
at HashTable.main(HashTable.java:119)
my code is exactly the same as up above except that i took out the static declaration in front of i and j, i commented out (not deleted) the j declaration, and put a new j declaration in the search method like this:
public boolean search(String w)
int j = 1; // <~~~~~this is the added line
int value
Please help