Question

I thought this would be very easy but I am having problems searching nodes from a text file.

The data from the text file follows:

1

2

3

4

5

The data is being stored in the String “word”. They are numbers to avoid complexity.

Issue is- is that it keeps on returning false when calling the search method.

public class Search
    {

        static int count;  // number of elements
        Search ()
    {
        count = 0;
    }


    static void inputdata (Node head, Node node) throws IOException
    {
        BufferedReader stdin = new BufferedReader (new InputStreamReader (System.in));
        BufferedReader reader = new BufferedReader (new FileReader ("Words.txt"));

        String word;
        String line = null;


        while ((line = reader.readLine ()) != null)
        {
            word = (line);
            node = new Node (word);
            node.next = head;
            head = node; // need to set the new head of the list to the node that was just inserted
            count++;
        }


        reader.close ();

        node = head;
        System.out.println ("Here is the list:");
        System.out.println ();
        do
        {
            System.out.println (node.data);
            node = node.next;
        }
        while (node != null);
        System.out.println ();
        System.out.println ();
    }




    static boolean Found (String search, Node head, Node node)  // recursive search method
    {
        boolean found;

        Node temp; // sets a termpoary node to the head
        node = head;
        temp = head;

        while (temp != null)
        {
            if (temp.data.equals (search))
                return true;
            temp = temp.next;

        }
        return false;
    }


    public static void main (String str[]) throws IOException
    {
        BufferedReader stdin = new BufferedReader (new InputStreamReader (System.in));
        DecimalFormat df = new DecimalFormat ("#");

        //Search list = new Search (); //calls list via constructor
        Node head = null;
        Node node = null;

        inputdata (head, node);



        System.out.println (count + " entries");

        String search, repeat;


        System.out.println ();
        System.out.println ("Which word do you want to search within the linked list?"); // returns true/false from a method
        search = stdin.readLine ();

        System.out.println (Found (search, head, node));

    }
}

other file (class):

public class Node
{
    Node next, prev;
    String data;

    public Node (String data)
    {
        this.data = data;
    }
}

Answer 1

Your problem is that your linked list only ever has one object in it at a time, since you are always setting node.next to head, and head to node. Therefore, you will always only print the same number (which I am going to guess, is exactly what you’re seeing).

What you need to do is to fix your insertion routine. Something like this should do (mind you that it’s untested)

Node prev;

while((line = reader.readLine()) != null) 
{
    word = line;
    node = new Node(word);
    node.next = null;

    if(head == null) {
        head = node;
    } 

    if(prev != null) {
        prev.next = node;
    }
    prev = node;

}