Thread: problem with Random()

Hello.

Iam having a problem with my code that makes the Random() part.

This is a code for a memory-game in android, but this question is more pure java than android sdk.

This is the code that i run right now.

ROW_COUNT = 3 and COL_COUNT = 4 
cards = new int [COL_COUNT] [ROW_COUNT];

private void loadCards(){ 
                try{ 
                int size = ROW_COUNT*COL_COUNT; 
 
 
                ArrayList<Integer> list = new ArrayList<Integer>(); 
 
 
                for(int i=0;i<size;i++){ 
                        list.add(new Integer(i)); 
                } 
 
 
                Random r = new Random(); 
 
 
                for(int i=size-1;i>=0;i--){ 
                        int t=0; 
 
 
                        if(i>0){ 
                                t = r.nextInt(i); 
                        } 
 
 
                        t=list.remove(t).intValue(); 
                        cards[i%COL_COUNT][i/COL_COUNT]=t%(size/2); 
                } 
            } 
                catch (Exception e) { 
                        Log.e("loadCards()", e+""); 
                } 
 
 
    }

The problem is that this will always make cards[0][0] = 5 becourse iam not requesting a random
number when i==0

if i try to change that

 if(i>0){ 
                               t = r.nextInt(i); 
                       }

to

 if(i>=0){ 
                               t = r.nextInt(i); 
                       }

This is wrong of course: r.nextInt(0) will throw IllegalArgumentException.

So my question is to you guys if there is a way round this problem of mine?

as you could see, iam new to this so please be gentle

Are you trying to make it so that the number is likely to get bigger the further you go?

All you have to do is make t = r.nextInt(i+1), so when i=0 it does r.nextInt(1) [Always 0!]

Are you trying to make each a random number?

Choose a max number and always call it like so: r.nextInt(100) [A psuedorandom number between 0 and 99]

Are you trying to make a set of unique values in a random order?

Look into the Collections.shuffle(List<?> list) method, although it would be a bit more complicated because it is a 2d array, but in effect you shuffle each deck in the array with Collections.shuffle(Arrays.asList(cards[i])) where i is a incrementing counter, then you shuffle Arrays.asList(cards) and bam, you got it.

Hello.

Iam trying to make it load the numbers two times like this in the logg:

03-23 21:42:38.519: INFO/loadCards()(359): size=12

03-23 21:42:38.529: INFO/loadCards()(359): card[3][2]=4

03-23 21:42:38.529: INFO/loadCards()(359): card[2][2]=0

03-23 21:42:38.529: INFO/loadCards()(359): card[1][2]=1

03-23 21:42:38.529: INFO/loadCards()(359): card[0][2]=4

03-23 21:42:38.529: INFO/loadCards()(359): card[3][1]=5

03-23 21:42:38.529: INFO/loadCards()(359): card[2][1]=5

03-23 21:42:38.529: INFO/loadCards()(359): card[1][1]=2

03-23 21:42:38.529: INFO/loadCards()(359): card[0][1]=1

03-23 21:42:38.529: INFO/loadCards()(359): card[3][0]=2

03-23 21:42:38.539: INFO/loadCards()(359): card[2][0]=3

03-23 21:42:38.539: INFO/loadCards()(359): card[1][0]=0

03-23 21:42:38.539: INFO/loadCards()(359): card[0][0]=3

This is the logg when i changed the code to t = r.nextInt(i+1) and it seems that it did the trick, iam going to test this some more but it seems good right now.

Thanks for the help.

It appears you want a set of psuedorandom numbers, in which it would be better to have that line something closer to

t = r.nextInt(6);

Which would be a random number between 0 and 5.