public static void main(String[] args) throws ParseException, IOException {

    BufferedReader br = new BufferedReader(new FileReader("primes.csv"));
    String line =  null;
    Hashtable<String, String> map = new Hashtable<String, String>(100);

    while((line = br.readLine()) != null){
        String str[] = line.split(",");

        map.put(str[0], str[1]);
    }
    br.close();
    System.out.println(map);

    int k;

    k = Integer.parseInt(JOptionPane.showInputDialog(f,"Enter an integer k whee"
            + " 3 < k < 1229: "));

    while (k <= 3 || k >= 1229){
       k = Integer.parseInt(JOptionPane.showInputDialog(f,"Sorry try again: "));
    }

    JOptionPane.showMessageDialog(f, "The "+ k +"th prime number is " + map.get(k));

}

String str[] = line.split(",");
...
map.put(str[0], str[1]);
...
int k;
...
map.get(k);