Random numbers not random

Question

I'm making a game in Java where I need dices. There are 3 dices for the attacker and 2 dices for the defencer. This is my code that randomize the eyes on all dices:

        if (attacker.getArmies() > 1)
            aDices[0] = random.nextInt(6) + 1;
        if (attacker.getArmies() > 2)
            aDices[1] = random.nextInt(6) + 1;
        if (attacker.getArmies() > 3)
            aDices[2] = random.nextInt(6) + 1;
        if (defencer.getArmies() > 0)
            dDices[0] = random.nextInt(6) + 1;
        if (defencer.getArmies() > 1)
            dDices[1] = random.nextInt(6) + 1;

But why are the numbers of the 'defence' dices mostly higher then the 'attack' dices?

I'm using the Random class from java.util.Random

Can you substantiate your claim?

Amir Rachum
– Amir Rachum

2012-10-13 13:11:30 +00:00
Commented Oct 13, 2012 at 13:11 — Amir Rachum
– Amir Rachum, Commented Oct 13, 2012 at 13:11
How many times do you mean my "mostly higher"?

Rohit Jain
– Rohit Jain

2012-10-13 13:11:52 +00:00
Commented Oct 13, 2012 at 13:11 — Rohit Jain
– Rohit Jain, Commented Oct 13, 2012 at 13:11
do you seed your random number generator?

Ionut Hulub
– Ionut Hulub

2012-10-13 13:12:30 +00:00
Commented Oct 13, 2012 at 13:12 — Ionut Hulub
– Ionut Hulub, Commented Oct 13, 2012 at 13:12
See dilbert.com/strips/comic/2001-10-25

JB Nizet
– JB Nizet

2012-10-13 13:12:53 +00:00
Commented Oct 13, 2012 at 13:12 — JB Nizet
– JB Nizet, Commented Oct 13, 2012 at 13:12
I know which Dilbert that is without even looking ;-)

DNA
– DNA

2012-10-13 13:17:50 +00:00
Commented Oct 13, 2012 at 13:17 — DNA
– DNA, Commented Oct 13, 2012 at 13:17

Difusio · Accepted Answer · 2012-10-13 13:18:31Z

Seeing that you are using exactly the same function for attack and defense, it's simply impossible that the outcome is structurally higher for attackers. What you could try to convince yourself is write a little function that rolls the dice a 100 times as attack and defense and calculate averages for that. And even then it is still possible that after a 100 times, attack wins a 100 times, unlikely, but possible. That's the nature of randomness.

This is a nice short read on randomness for some background information:

http://engineering.mit.edu/live/news/1753-can-a-computer-generate-a-truly-random-number

Marcus Tik · Accepted Answer · 2012-10-13 13:15:19Z

0

Maybe you should use the Random class in combination with timestamps from your PC clock. It's called a seed for the randomizer.

answered Oct 13, 2012 at 13:15

Marcus Tik

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Comments

Joachim Isaksson · Accepted Answer · 2012-10-13 13:33:30Z

It would seem that the code you're showing is giving more of an advantage to the defender than original Risk does;

if (attacker.getArmies() > 1)          // 1 army will never roll the dice
    aDices[0] = random.nextInt(6) + 1;

The attacker gets 1 dice roll per army (1-3) he attacks with. You're giving him 0-2. That would mean that an attack with one army will never succeed.
The defender gets 1 dice roll per army (1-2) he defends with. You're giving him 1-2.

That would tilt the game more towards the defender than original risk does, all without getting biased random numbers.

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