Token Generator Using Threads I have a class that I am using to generate 10 character alphanumeric 'tokens' (Strings) and writing them to a txt file. 

I would like to be able to generate as many as possible as quickly as possible without producing any duplicates. This is what I have so far:

import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Random;

public class TokenGenerator  {

  public static void main(String[] args) {

    for (;;) {
         getSaltString();
    }
 }

public static void getSaltString() {
    String SALTCHARS = "ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";
    StringBuilder salt = new StringBuilder();
    Random rnd = new Random();

    while (salt.length() &lt; 10) { // length of the random string.
        int index = (int) (rnd.nextFloat() * SALTCHARS.length());
        salt.append(SALTCHARS.charAt(index));
    }
    String saltStr = salt.toString();
    writer(saltStr);
}

public static void writer(String code) {
    try {
        File file = new File("codes.txt");
        PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter(file, true)));
        out.println(code);
        out.close();

    } catch (IOException e) {
       System.out.println("Dead");
    }
  }
}


I was wondering,

A: Is this an efficient way of generating the tokens?

B: How can I call this method using threads to generate them faster
Bug 1

Requirement is 'without producing any duplicates'. You have not exactly implemented this (although the chances of happening are really small)

Bug 2

You have no condition of exiting. The program will run forever, and might have inconsistent behaviour if you terminate it externally.  

A: Is this an efficient way of generating the tokens?

It can be more efficient. 


You can keep the File and Writers open instead of opening each time.
You can reuse the new Random() instead of creating one each time, or..
...use int randomNum = ThreadLocalRandom.current().nextInt(min, max + 1);
You can use a fixed for loop instead of checking the salt.length().


Also use try-with-resources.

B: How can I call this method using threads to generate them faster

As you write to file, this process will finally be I/O bound, so there is probably no real gain from multi-threading.