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.

Code :

---

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

---

Code :

---

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

Code :

---

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

---

to

Code :

---

 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 :o

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.