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Thread: PLEASE HELP! (hashtable in Java)

  1. #1
    Junior Member hedyeh's Avatar
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    Default PLEASE HELP! (hashtable in Java)

    Dear all,

    I have a problem with my code. There are some bugs which I don't know how to fix!

    The code is supposed to use the division method of hashing to store the data values into hash tables with different table sizes, and be able to search for a specific number. The linear probing is used to minimize the collisions. I used the methods provided in my course textbook (hash, add and get). So the methods are correct.

    The compiler cannot compile my code and gives for the line:

    tablesize7.add((Hashable)start);

    the following error:

    inconvertible types.
    found: int; required: Hashtable.hashable

    but I cannot define variable start as a Hashable. Right? Because when I do that, then the compiler cannot calculate the following:

    return(element%max_elements);


    Here's the code:

    package Hashtable;
     
     
    public interface Hashable
    {
         int hash();
    }


    package Hashtable;
     
    public class HashDataset implements Hashable {
     
       static int element; 
       static Hashable list[];
       static int max_elements;   
       protected int numElements = 0;
       static int tableSize;
       static int start;
     
       public int hash() { 
          return(element%max_elements);
       }
     
       public void add (Hashable element)  {
     
         int location = element.hash();
     
          while(list[location]!=null) {
              location = (location + 1) % list.length;
              list[location]=element;
              numElements++; 
      } 
    } 
     
      public Hashable get(Hashable element) {
     
         int location = element.hash();
     
        while(list[location]!=element)
           location = (location + 1) % list.length;
     
        return (Hashable)list[location];
    }
     
     
     
    public HashDataset(int start, Hashable list[], int tableSize)  {
     
          element=start;
          this.list = list;
          max_elements = tableSize;
     
      }
     
    public static void main(String[] args) {
     
       HashDataset tablesize7 = new HashDataset(1500, new Hashable[150], 7); 
     
       for(int i=0; i<100; i++)  {  
         tablesize7.hash();
         tablesize7.add((Hashable)start);
         System.out.println(start);
     
     
    }
    }
    }


  2. #2
    Super Moderator Norm's Avatar
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    Default Re: PLEASE HELP! (hashtable in Java)

    But the program doesn't work!
    Please explain what the code does and what the problem is.

    Please edit your post and wrap your code with code tags:
    [code=java]
    <YOUR CODE HERE>
    [/code]
    to get highlighting and preserve formatting.
    If you don't understand my answer, don't ignore it, ask a question.

  3. The Following User Says Thank You to Norm For This Useful Post:

    hedyeh (April 11th, 2013)

  4. #3
    Member Chris.Brown.SPE's Avatar
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    Default Re: PLEASE HELP! (hashtable in Java)

    The problem is on line tablesize7.add((Hashable)start); "start" is an int so it cannot be cast to "Hashable".

    --- Update ---

    It seems to me like you're using your interface incorrectly. Your dataset isnt what is "hashable", the data should be. If this is what you're trying to do, maybe you should be making a class called HashableInt and have that implement "Hashable".
    Writing code is your job, helping you fix and understand it is mine.

    <-- Be sure to thank and REP (Star icon) those who have helped you. They appreciate it!

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