Select different random elements from an ArrayList of array of strings in java

Question

I am Rookie. I have to select randomly different elements from an ArrayList which has an array of strings. I tried couple different ways but it is selecting the same array every time.Here are the ways I tried.

 public static void RandomSchedules(ArrayList<String[]> list)
{
    Random randomizer = new Random();
    for(int i=1; i<11; i++)
   {

    String[] random = list.get(new Random().nextInt(list.size()));
    System.out.println("Random Schedule " +  ":" + Arrays.toString(random));
    }
}

I also tried this in the above code.

   String[] random = list.get(randomizer.nextInt(list.size()));

But the result is same.

This is the other approach I have tried from Stack Overflow

 public static List<String[]> pickNRandom(ArrayList<String[]> lst, int n) {
List<String[]> copy = new LinkedList<String[]>(lst);
Collections.shuffle(copy);
return copy.subList(0, n);
 }

I am calling the above function as,

    List<String[]> randomPicks = pickNRandom(lst, 10);

Could anyone guide me how to get different elements.

Sounds to me like you might have duplicate arrays. Did you check the contents? — shmosel
– shmosel, Commented Oct 31, 2017 at 18:35

sma · Accepted Answer · 2017-10-31 18:32:20Z

3

You don't use your randomizer object, but create a new one each time in the loop. So use the one you created (avoiding the new Random call everytime). Try:

public static void RandomSchedules(ArrayList<String[]> list)
{
    Random randomizer = new Random(System.currentTimeMillis());
    for(int i=1; i<11; i++)
    {
        String[] random = list.get(randomizer.nextInt(list.size()));
        System.out.println("Random Schedule " +  ":" + Arrays.toString(random));
    }
}

answered Oct 31, 2017 at 18:32

sma

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1 Comment

sma Over a year ago

What is your input list? If it just one String [] (list.size() == 1), then it will do that, but multiple string[] in your list will yield variable outputs

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