Question

another question to put out there. I was working on an assignment to create hash functions and all that jazz, and i have stumbled across a small problem.

Line 35:21, where it reads arrpos += prearrpo & ______,

in my head works… What im trying to do is access arr.length from the HashTable() method. I’ve read around, suggestions with needing to creat an object of size arr.length; however in my mind, this seems overly complicated-

Is there another way i can access the variable in the HashTable method, but inside the insert method?

Another not so important question involves the giant block of if() statements in the letter(char c) class; im certain there must be a shorter way of doing this… I would have initially used the ascii values; but the specifications were quite particular about using the values 1-26 for lower/upper case letters-

Thanks

import java.io.*;

public class HashTable {

    public HashTable() {
        //Create an array of size 101
        String arr[] = new String[101];
        //System.out.println("Size1: ");
    }

    public HashTable(int tsize) {
        int size = 2 * tsize;
        //System.out.println("Size: " + size);
        boolean isPrime = checkPrime(size);
        //System.out.println("IsPrime: " + isPrime);
        while (isPrime == false) {
            //System.out.println("Size: " + size);
            size++;
            isPrime = checkPrime(size);
        }
        //System.out.println("Size: " + size);
        String arr[] = new String[size];
    }

    public boolean insert(String line) {

        String str = line;
        char[] ch = str.toCharArray();
        int slen = str.length();
        int arrpos = 0;
        int hash = slen;
        for (int i = 0; i < slen; i++) {
            double prearrpo = letter(ch[i]) * Math.pow(32, (hash - 1));
            arrpos += prearrpo % arr.length();
            hash--;

        }
        System.out.println(arrpos);
        System.out.println("array size:");
        System.out.println();
        return false;

    }

    private int letter(char c) {
        char ch = c;
        if (ch == 'A' || ch == 'a') {
            return 1;
        }
        if (ch == 'B' || ch == 'b') {
            return 2;
        }
        if (ch == 'C' || ch == 'c') {
            return 3;
        }
        if (ch == 'D' || ch == 'd') {
            return 4;
        }
        if (ch == 'E' || ch == 'e') {
            return 5;
        }
        if (ch == 'F' || ch == 'f') {
            return 6;
        }
        if (ch == 'G' || ch == 'g') {
            return 7;
        }
        if (ch == 'H' || ch == 'h') {
            return 8;
        }
        if (ch == 'I' || ch == 'i') {
            return 9;
        }
        if (ch == 'J' || ch == 'j') {
            return 10;
        }
        if (ch == 'K' || ch == 'k') {
            return 11;
        }
        if (ch == 'L' || ch == 'l') {
            return 12;
        }
        if (ch == 'M' || ch == 'm') {
            return 13;
        }
        if (ch == 'N' || ch == 'n') {
            return 14;
        }
        if (ch == 'O' || ch == 'o') {
            return 15;
        }
        if (ch == 'P' || ch == 'p') {
            return 16;
        }
        if (ch == 'Q' || ch == 'q') {
            return 17;
        }
        if (ch == 'R' || ch == 'r') {
            return 18;
        }
        if (ch == 'S' || ch == 's') {
            return 19;
        }
        if (ch == 'T' || ch == 't') {
            return 20;
        }
        if (ch == 'U' || ch == 'u') {
            return 21;
        }
        if (ch == 'V' || ch == 'v') {
            return 22;
        }
        if (ch == 'W' || ch == 'w') {
            return 23;
        }
        if (ch == 'X' || ch == 'x') {
            return 24;
        }
        if (ch == 'Y' || ch == 'y') {
            return 25;
        }
        if (ch == 'Z' || ch == 'z') {
            return 26;
        }
        return 0;
    }

    public boolean lookUp(String string) {
        // 
        return false;
    }

    public String getNum() {
        // 
        return null;
    }

    public int length() {

        return 0;
    }

    private static boolean checkPrime(int size) {

        if (size % 2 == 0) {
            return false;
        }
        double c = Math.sqrt(size);
        for (int i = 3; i < c; i += 2) {
            if (size % i == 0) {
                return false;
            }
        }



        return true;
    }
}

Answer 1

public HashTable() is a constructor. Your arr[] should actually be a private member of your class and you should initialize it in all constructors or make sure you never access without intializing it.

public class HashTable {

    private String[] arr;

    public HashTable() 
    {
        //Create an array of size 101
        arr[] = new String[101];
        System.out.println("Size1: ");
    }
etc...