Question

This is kind of a weird question. I’d like to write a Java function that will either return true or false. It will ALWAYS return either true or false for the same computer, even if the program has been purged from the computer and reinstalled (that is, no state is allowed.) It will return the same value no matter where in the program it is called, what time it is, if it’s a Tuesday, etc.

My second requirement is that for all of the computers in the world it there should be anywhere from a 50/50 to a 30/70 split in what the function returns. That is, at least 30% of computers need to generate the less-likely result of the function.

My third requirement (the tricky one) is that what causes the true/false split won’t be obvious to users. So splitting along operating system lines isn’t okay, since that’s obvious.

Any thoughts?

Update: True, “same computer” doesn’t have much meaning since computers are made of changeable parts. It’s fine for the value to change if a piece of hardware is replaced.

Answer 1

Well, the most simple solution would be to just use the last digit of the mac address to return
true or false based on if its even or odd.
This will ensure that on the same machine it always returns the same for a machine and it will return true on half the machines in the world.

import java.net.*;


/**
 *
 * @author nick
 */
public class HardwareTruthGen {

   //Instance Variables 
    static InetAddress addr;
    static NetworkInterface net;
    static byte[] macAddr;
    static boolean hardware;

   static {

       try{  
        addr = InetAddress.getLocalHost();
        net = NetworkInterface.getByInetAddress(addr);
        macAddr = net.getHardwareAddress();

        //If mac address ends in an even number return true otherwise return false 
        if((macAddr[(macAddr.length - 1)] % 2) == 0)
            hardware = true;
        else
            hardware = false;
      }
      catch (Exception ex){

      }
    }

   public static boolean macTrue(){ return hardware;}

 }