replace - Arraylist - Set/ add method usage - Java

Question

I have an Arraylist of integers. My requirement is to determine if the arraylist HAS an element existing at the specified index.If YES, then a value should be set to that index (using set method), else a value should be added to that index location(using add method)

Finding it a bit difficult to handle the above condition in my java code.Please help.

Here's what I have so far:

    ArrayList<Integer> tempArray = new ArrayList<Integer>();
        int counter = 0;
        int tempValue = 0;
    For LOOP -
      if (//certain conditions are satisfied){

      tempValue = calculateNewValue();
      tempArray.add(counter, tempValue); //Need some logic here to determine if its a set or add method to be used
    }
if (//some other conditions are satisfied){
       counter++;
}
    end For LOOP

Answer 1

set method replaces the element in the specified position with the new element. But in add(position, element) will add the element in the specified position and shifts the existing elements to right side of the array .

ArrayList<String> al = new ArrayList<String>();

    al.add("a");
    al.add(1, "b");
    System.out.println(al);

    al.set(0, "c");
    System.out.println(al);

    al.add(0, "d");
    System.out.println(al);

---------------Output -------------------------------------

[a, b]

[c, b]

[d, c, b]