Creating a hashtable but it fails at this point. Need help as to why it fails

Question

So I am trying to implement a hashtable using an array of linklists. For practice I implemented my own linklist and now I am trying to implement the hash table. Now the hash function is very simple, it just takes the integer value of the char and mods it by the arraysize of the hasharray.

In the below code, I have commented the place where it errors out. It seems to hash the character value just fine, however when I try to insert it into the array of linklists, that's where it crashes.

I have tested the linklist class and that works fine. The error I get along with the system.out.println statements are:

Runtime error time: 0.07 memory: 380160 signal:-1
Created HashTable
hashInsert
hashFunction
2
hashFunctionAfter2f

Java Code: for class LinkListPractice:

class LinkListPractice{

    public static void main (String[] args) throws java.lang.Exception
    {
        // your code goes here

        HashTable testHashTable = new HashTable(10);
        System.out.println("Created HashTable");

        System.out.println(testHashTable.hashInsert('f'));

    }
}

Java Code: for class HashTable:

class HashTable{

    LinkList[] hashArray;
    int arraySize;

    public HashTable(int size){
        hashArray = new LinkList[size];
        arraySize = size;
    }

    public int hashInsert(char value){
        System.out.println("hashInsert");
        int index = hashFunction(value);
        System.out.println("hashFunctionAfter"+index+value);
            /********************************************************
        code gets to here but it fails after printing the above.
        I think somehow the hashArray is not initialized 
            so it is failing trying to call the insertLink method
        can someone tell me why it is failing here?
            *********************************************************/
        hashArray[index].insertLink(value);

        return index;
    }

    public int hashFunction(char value){
        System.out.println("hashFunction");
        int index = (value % arraySize);
        System.out.println(index);

        return index;
    }

}

Java Code: for class Link:

class Link{
    public char value;
    public Link next;
    public Link prev;

    public Link(char data){
        this.value = data;
        this.next = null;
        this.prev = null;
    }
}

Java Code: for class LinkList:

class LinkList{
    public Link head;
    public Link tail;

    public LinkList(){
        head = null;
        tail = null;
    }

    public void insertLink(char data){
    System.out.println("insertLink" + data);

        Link newLink = new Link(data);

        if (head == null && tail == null){
            head = newLink;
            tail = newLink;
        }
        else if (head == tail){
            head.next = newLink;
            newLink.prev = head;
            tail = newLink;
        }
        else if (head != tail){
            tail.next = newLink;
            newLink.prev = tail;
            tail = newLink;
        }
    }

    public void printLinkList(){
        Link currentLink = head;

        while(currentLink != null){
            System.out.println(currentLink.value);
            currentLink = currentLink.next;
        }
    }

    public void printLinkListPrev(){
        Link currentLink = head;

        while(currentLink != null){
            if(currentLink.prev == null){
                System.out.println("HEAD");
                currentLink = currentLink.next;
            }
            else{
                System.out.println(currentLink.prev.value);
                currentLink = currentLink.next;
            }
        }
    }
}

Sorry about that. When I run it through, I get this: Runtime error time: 0.07 memory: 380160 signal:-1 Created HashTable hashInsert hashFunction 2 hashFunctionAfter2f — froncthetonc, Mar 27 '14 at 05:20
I think there are some issues with Arraylist array creation. refer this: http://stackoverflow.com/questions/15193229/can-you-create-an-array-of-linked-lists-in-java — Aditya Peshave, Mar 27 '14 at 05:23
When I declare the array of LinkLists: LinkList[] hashArray; and then in the constructor I initialize it: hashArray = new LinkList[size]; does it also call the constructor for all the LinkList objects in that array? I'm thinking this may be the problem that when I try to call the insertLink method, the actual LinkList object is not constructed. Or is that wrong and when I construct the hashArray = new LinkList[size], does it also call the constructor of all the LinkList objects within that array?? — froncthetonc, Mar 27 '14 at 05:34

score 0 · Accepted Answer · answered Mar 27 '14 at 05:32

0

You need to initialize the objects in the hashArray array.

        hashArray[index] = new LinkList();
        hashArray[index].insertLink(value);

Side note: when commenting in your file, don't use

/** text **/

since that is reserved for Javadoc.

answered Mar 27 '14 at 05:32

user1803551

12,965
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Thanks. That was the issue. For some reason I thought when I created and initialized an array of LinkList, I thought it would call the constructor of each one but I guess not. Thanks again. – froncthetonc Mar 27 '14 at 05:40
Objects in an array are not initialized when the array is created for many reasons (such as they can be abstract classes). – user1803551 Apr 23 '14 at 16:05

Creating a hashtable but it fails at this point. Need help as to why it fails

1 Answers1