Double Iteration Over a Hashmap

I'm using a hashmap to hold multiple Player objects for a multi-player game. In one section of my code, I need to check the distances from each player to every other player. I learned how to iterate over a hashmap, but things seem to go very wrong when I try two levels of nested iteration over the same map.

Code:

---

Iterator a = player.entrySet().iterator();
               
while (a.hasNext())
{
        Map.Entry aMe = (Map.Entry)a.next();
        Player myAPlayer = (Player) aMe.getValue();
                                   
        Iterator b = player.entrySet().iterator();
                                   
        while (b.hasNext())
        {
                Map.Entry bMe = (Map.Entry)b.next();
                Player myBPlayer = (Player) bMe.getValue();

                // First make sure that myAPlayer and myBPlayer are not the same,
                // then do something here with both players.
        }
}

---

I am assuming what I am doing here is incorrect. What would be the simplest method to perform a two level nested iteration on a hashmap?

Thank you in advance for your time.

I am no pro at this, and don't know if there is a standard way to do this, but one way that may work is to create a List out of the map's keySet, and then iterate over the list in a pair of nested for loops. For e.g., if the Map Keys and Values were Strings and this were a generic map:

Code:

---

      List<String> list = new ArrayList<String>(map.keySet());
      for (int i = 0; i < list.size() - 1; i++) {
        for (int j = i + 1; j < list.size(); j++) {
            System.out.printf("[%s, %s]%n", map.get(list.get(i)), map.get(list.get(j)));
        }
      }

---