My random integer generator.

[Aces Kok Ben]

Hello guys it's me again. I'm working on this project recently and I wanted to created a algorithm that can randomly generate many sets of integer, however the codes kinda "stuck" somehow. Please take a look at my code:

import java.util.Random;

public class OneTimePass {

	String Otp;
	int counter = 0;
	int firstPos;
	int secPos;

	public void setFirstPos(int firstPos){
		this.firstPos = firstPos;
	}

	public int getFirstPos(){
		return firstPos;
	}

	public void setSecPos(int secPos){
		this.secPos = secPos;
	}

	public int getSecPos(){
		return secPos;
	}

	public int firstPosGen(){
		//Generation of the integer on the first position of the PIN
		int gen1;

		Random rd = new Random();
		gen1 = rd.nextInt(10);
		
		return gen1;
	}

	public int secondPosGen(int firstPos){
		//Generation of the integer on the second position of the PIN
		int gen2 = 0;
		boolean odd = false;
		boolean even= false;
		Random rd = new Random();
		
		System.out.println("firstPos: " + xfirstPos);

		//If the integer at the first position is < than 5 the return integer on the second position will be an ODD number.
		// if > 5 then return a integer that is an EVEN number.
		//CONTINUE FROM HERE:

		if (firstPos < 5){
			do{
				gen2 = rd.nextInt(10);
				if((gen2 % 2) == 0){
					odd = false;
				}
				else {
					odd = true;
					System.out.println("(TESTING)FirstPos value: " + firstPos);
					System.out.println("Odd Number generated at second position: " + gen2);
				}
			}while(odd = false);

		}
		else {
			do{
				gen2 = rd.nextInt(10);
				if((gen2 % 2) != 0){
					even = false;
				}
				else{
					System.out.println("(TESTING)FirstPos value: " + firstPos);
					System.out.println("Even Number generated at second position: " + gen2);
					even = true;
				}
			}while(even = false);
		}

		return gen2;
	}


	public static void main (String [] args){
		
		int temp;

		System.out.println("This is Main.");
		OneTimePass OTPobj = new OneTimePass();

		//Generating a random integer using firstPosGen method, and setting it on the First position on the PIN
		temp = OTPobj.firstPosGen();
		OTPobj.setFirstPos(temp);
		System.out.println("(TESTING)First Position: " + OTPobj.getFirstPos());
		
		OTPobj.secondPosGen(temp);
		System.out.println("TESTING");


	}

}

First time when I run the program on eclispe, the output was:

"This is Main.
(TESTING)First Position: 4
firstPos: 4
TESTING"

I was fascinated by the output. It was supposed to generate another number (...Odd Number generated at second position: + gen2), which is an Odd number for the second position, however, the program stuck there? It should generate an integer that is Odd. I gave another chance and ran the program several times again, this time the output was:

"This is Main.
(TESTING)FirstPos value: 4
Odd Number generated at second position: 9
TESTING"

This is the correct output that I was expecting but why is it working good at times and not at other times? What I was expecting was:

1. If firstPos (an integer), is bigger than 5, than the number generated at the second position should be an ODD no.
2. else, it should be an EVEN number.

What happen? Is my logic flow correct? I spend quite sometime on this because Im not good in programming and now it's screwing me up

[Campbell Ritchie]

If there is any relation between the first and second digits, then you are not generating random numbers.

Never, never, never try using == true and == false. You get some nasty errors if you mistakenly write = for ==. As you have done in two places . . .
Don't write if ( . . . ) b = true; else b = false; Write

gen2 = random.nextInt(10);
odd = (gen2 & 1) == 1;

The & 1 tests whether the last bit in the number is 1, and is a much quicker way to test for odd and even numbers. it only works for & 1, & 3, & 7, etc, and unlike % will return a positive result from negative arguments.
Why have you got booleaen values odd and even? You should not have both, since ∀i • odd == !even

[Wouter Oet]

Why the complex logic? Why not just generate a random number and if it is odd and you want even subtract one?

[Aces Kok Ben]

Campbell Ritchie wrote:If there is any relation between the first and second digits, then you are not generating random numbers.

Never, never, never try using == true and == false. You get some nasty errors if you mistakenly write = for ==. As you have done in two places . . .
Don't write if ( . . . ) b = true; else b = false; Write

gen2 = random.nextInt(10);
odd = (gen2 & 1) == 1;

The & 1 tests whether the last bit in the number is 1, and is a much quicker way to test for odd and even numbers. it only works for & 1, & 3, & 7, etc, and unlike % will return a positive result from negative arguments.
Why have you got booleaen values odd and even? You should not have both, since ∀i • odd == !even

I wanted to write a class to create a unique ONE-TIME-PIN. And yes, now i realised: it should be == instead of =

[Campbell Ritchie]

Aces Kok Ben wrote:[ . . . it should be == instead of =

No, it should be nothing at all. If you want it to be false, you write do { ... } while (!done); or if (!boo) { ... } or similar.

[Jesper de Jong]

Wouter Oet wrote:Why the complex logic? Why not just generate a random number and if it is odd and you want even subtract one?

Or, if you want only even random numbers, just generate a random number and multiply it by 2.