Random ints in an array and arraylist

Question

So i have two methods to create a randomized array and arraylist with 100 random integers. For some reason only the arraylist works though. Not sure what is wrong. Can someone take a look at it? I really don't know why it doesn't work. Is there a better way to randomize an array?

public static int[] gen1()
  {
    int[] no = new int[100];
    for(int i=0;i<no.length;i++)
    {
        no[i] =(int)(Math.random());
    }
    return no;
}   

public static ArrayList<Integer> gen2()
{
    ArrayList<Integer> oh = new ArrayList<Integer>();
    Random random = new Random();
    for (int i = 0; i < 100; i++)
    {
        oh.add(random.nextInt());
    }
    return oh;
}

public static void main(String[] args)
{   
    System.out.println("Original Array:");
    System.out.println(gen1());
    System.out.println("Original List:");
    System.out.println(gen2());
}

Why `(int)(Math.random())` in one case and `Random#nextInt` in the other? What does `Math.random()` do? Why do you think so? — Sotirios Delimanolis, Nov 28 '15 at 18:48

score 0 · Answer 1 · answered Nov 28 '15 at 18:49

0

Math.random() returns a double between 0 and 1 (exclusive), so casting it to int will always return 0. That's the reason your array will contain only 0s.

On the other hand, random.nextInt(), used to populate the ArrayList can return any of the possible int values.

answered Nov 28 '15 at 18:49

Eran

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Ok, what do i use then? How do I put random ints into my array? – user5344755 Nov 28 '15 at 18:51
@user5344755 Use the same code you used for generating random ints for the ArrayList. – Eran Nov 28 '15 at 18:52
I just tried this and it still didn't work... public static int[] gen1() { Random random = new Random(); int[] no = new int[100]; for(int i=0;i – user5344755 Nov 28 '15 at 18:55
@user5344755 You haven't defined _didn't work_. Are you just having trouble printing the array? – Sotirios Delimanolis Nov 28 '15 at 18:56
@user5344755 What do you mean by doesn't work? You should note that `System.out.println(gen1());` is not the correct way to print an array. Try `System.out.println(Arrays.toString(gen1()));` – Eran Nov 28 '15 at 18:56
It wasn't printing out correctly I guess. I got it to work thank you. – user5344755 Nov 28 '15 at 18:59

Random ints in an array and arraylist

1 Answers1