Is there a way I can convert a[indexOfMin] = a[startIndex] into ArrayList form? I can't seem to properly do so

Question

Towards the bottom of my program I am trying to convert the selection sort algorithm that I had from an array to ArrayList. Those two lines that are producing errors were previously a[indexOfMin] = a[startIndex]; and a[startIndex] = min;. I tried changing them to a.get(indexOfMin) = a.get(startIndex); and a.get(startIndex) = min; but that does not compile. Thank you for any and every bit of help!

class SortDouble
{
    public static void main(String[] args)
    {
        int n = 10;
        ArrayList<Double> a = new ArrayList<Double>();
        Random r = new Random();

        for (int i = 0; i < n; i++)
            a.add(r.nextDouble());

        selectionSort(a);

        for (int i = 0; i < n; i++)
            System.out.println(a.get(i));

    }

    public static void selectionSort(ArrayList<Double> a)
    {
        int n = 10;
        for (int startIndex = 0; startIndex < n - 1; startIndex++)
        {
            double min = a.get(startIndex);
            int indexOfMin = startIndex;
            for (int j = startIndex + 1; j < n; j++)
                if (a.get(j) < min)
                {
                    min = a.get(j);
                    indexOfMin = j; 
                }
            a.get(indexOfMin) = a.get(startIndex); // error here
            a.get(startIndex) = min; // error here
        }
    }
}```

Answer 1

To update the value at a specific index in a Arraylist, we use set method.
Change the two lines which were causing error to:

a.set(indexOfMin, a.get(startIndex));   // a[indexOfMin] = a[startIndex];
a.set(startIndex, min); // error here   // a[startIndex] = min;