Choosing a random number

Question

How can I randomly choose a number from a list of given numbers in Java?

I have only these 5 numbers: 1000, 2000, 3000, 4000, 5000

Now I have to select any one number from this set of numbers randomly.

My code to try this

int ar[] = new int[4];
ar[0] = 1000;
ar[1] = 2000;
ar[2] = 3000;
ar[4] = 4000;

int randomArrayIndex = num.nextInt(ar.length);

What is `num`? And what is the result of your code (which is not complete I guess)? Please post a complete code that you have tried. — Rohit Jain, Jan 31 '13 at 15:38
Given that `num` is an instance of the `Random` class, you're doing it quite right. What is _not_ working for you with this code? — Petr Janeček, Jan 31 '13 at 15:40
I'm assuming `ar[4]=4000;` should read `ar[3]=4000`, as index `4` does not exist (the _4th_ index does, but that is index **3**, because they start from 0). — Clockwork-Muse, Jan 31 '13 at 16:39

score 6 · Accepted Answer · answered Jan 31 '13 at 15:39

6

int randomArrayIndex = new Random().nextInt(ar.length); 
int number = ar[randomArrayIndex];

answered Jan 31 '13 at 15:39

Nikolay Kuznetsov

It can generate same number more than once. – Achintya Jha Jan 31 '13 at 15:43
1

@AchintyaJha, so what? There is not requirement like that. – Nikolay Kuznetsov Jan 31 '13 at 15:44

score 1 · Answer 2 · answered Jan 31 '13 at 15:39

1

Try this

public static int myRandom(int low, int high) {
    return (int) (Math.random() * (high - low) + low);
}

and set low and high to 0 and 4.

answered Jan 31 '13 at 15:39

Roman Holzner

+1 or you can have a low of 1 and a high of 5 and multiple by 1000 – Peter Lawrey Jan 31 '13 at 15:45

Achintya Jha · Answer 3 · 2013-02-01T10:23:31.867

1

If you don't want to repeat numbers from original array:

 Integer [] array = {1000,2000,3000,4000};
 Collections.shuffle(Arrays.asList(array));

If only one random number is required from the given array .

int[] array = {1000,2000,3000,4000};

int randomNumber = array[(int)(Math.random()*array.length)];

edited Feb 01 '13 at 10:23

answered Jan 31 '13 at 15:42

Achintya Jha

@Destrictor Its not a good approach ? – Achintya Jha Jan 31 '13 at 15:49
1

It seems a bit wasteful if you only want the one number :). If he needs all of them in a random order though, this is a very nice solution. – Destrictor Feb 01 '13 at 08:32
@Destrictor Yes, I wrote the conditions for both case. Thanks. – Achintya Jha Feb 01 '13 at 10:24
@NikolayKuznetsov Can you explain why Math.random() not recommended ? – Achintya Jha Feb 02 '13 at 08:21
1

@NikolayKuznetsov I used and it works.... – Ameer Feb 02 '13 at 08:52
@NikolayKuznetsov What difference does it make on this array? No difference at all. – Achintya Jha Feb 02 '13 at 09:16
@NikolayKuznetsov Yes, so what? We cant edit ? I got comment on my previous answer and I edited. – Achintya Jha Feb 02 '13 at 09:19
@NikolayKuznetsov You downvoted me without any reason. And why should I copy and paste your answer. Google works on my computer. – Achintya Jha Feb 02 '13 at 09:28
let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/23831/discussion-between-achintya-jha-and-nikolay-kuznetsov) – Achintya Jha Feb 02 '13 at 09:31
1

@NikolayKuznetsov Sir you think you are good. But I selected and accepted that answer due to the fulfillment of my query. And I just want a solution and not a lecture. Got it – Ameer Feb 02 '13 at 10:52
@NikolayKuznetsov int[] array = {1000,2000,3000,4000}; int randomNumber = array[(int)(Math.random()*array.length)]; – Ameer Feb 02 '13 at 14:17

3 Answers3