dealing with random numbers in android

Question

I want to ask how to generate non repeating numbers in my buttons. I want to generate a non repeating number because whenever i run my project it shows all the same numbers.

Below is the code I have:

int arr1[]={1,2,3,4,5,6,7,8,9,10};
int num=(int)(Math.random()*10);
    one.setText(""+arr1[num]);
    two.setText(""+arr1[num]);
    three.setText(""+arr1[num]);

I want to know how to set the one,two and three buttons not having the same value if possible.

Have you tried calling `Math.random` three times, once for each button? — Dennis Meng, Aug 27 '13 at 16:11
possible duplicate of [Non repeating random numbers](http://stackoverflow.com/questions/4897410/non-repeating-random-numbers) — chrylis -cautiouslyoptimistic-, Aug 27 '13 at 16:12
@chrylis Not really, it looks like the other question was trying to shuffle and running into seed issues. This time around, the poster isn't even calling `random()` or equivalent more than once. — Dennis Meng, Aug 27 '13 at 16:17
@DennisMeng Right, but the entire approach here is wrong. Repeatedly calling `random()` (not even `nextInt()`!) won't produce the non-repeats he wants. — chrylis -cautiouslyoptimistic-, Aug 27 '13 at 16:18

Arnaud Denoyelle · Answer 1 · 2013-08-27T16:34:58.587

Your code is nearly equivalent to :

int arr1[]={1,2,3,4,5,6,7,8,9,10};
int num = arr1[(int)(Math.random()*10)];
one.setText(""+num);
two.setText(""+num);
three.setText(""+num);

That's why you see 3 times the same number.

You should use Random#nextInt(int n) instead of your array and generate 3 random numbers :

Random r = new Random();
one.setText(Integer.toString(1 + r.nextInt(10)));
two.setText(Integer.toString(1 + r.nextInt(10)));
three.setText(Integer.toString(1 + r.nextInt(10)));

And if you want your numbers to be non-repetitive, you can for example use a Set :

Random r = new Random();
Set<Integer> randomNumbers = new HashSet<Integer>();
while(randomNumbers.size() <= 3){
  //If the new integer is contained in the set, it will not be duplicated.
  randomNumbers.add(1 + r.nextInt(10));
}
//Now, randomNumbers contains 3 differents numbers.

sealz · Answer 2 · 2013-08-27T16:19:55.900

In android you can generate a random number like this. If needed you can use a min and max instead of an array.

int min = 1;
int max = 10;
Random r = new Random();
int someRandomNo = r.nextInt(max - min + 1) + min;
one.setText(""+someRandomNo);

To double check that you dont get the same random number you will just need some logic that checks if it has already been generated. You can stick to your array and remove that number before the next call. Or just check a stored integer before you call again if you use min and max.

Sajal Dutta · Answer 3 · 2013-08-27T16:26:51.760

0

private int previous = -1000; // Put a value outside your min and max

/**
 * min and max is the range inclusive
 */
public static int getRandomNumber(int min, int max) {

    int num;

    do {

        num = min + (int)(Math.random() * ((max - min) + 1));

    } while(previous == num); // Generate a number that is not the same as previous

    previous = num;

    return num;    
}

edited Aug 27 '13 at 16:26

answered Aug 27 '13 at 16:21

Sajal Dutta

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With this, you can generate `1, 3, 1`. This is not repetitive but contains duplicates. I think that the OP does not want this. – Arnaud Denoyelle Aug 27 '13 at 16:25
@ArnaudDenoyelle In that case, I got the question wrong. Oh well.. – Sajal Dutta Aug 27 '13 at 16:27

dealing with random numbers in android

3 Answers3