How is the storage of lists implemented in a HashMap structure?

In Java, the HashMap structure stores key-value pairs, where keys are stored in buckets based on the hash code of the key.

If the value is a list (for example, List<T>), then HashMap simply stores a reference to this list as the value. The list itself does not have any special integration with HashMap — it is just a regular object that can be retrieved, modified, or replaced.

Example:

HashMap<String, List<Integer>> map = new HashMap<>();
map.put("numbers", new ArrayList<>(Arrays.asList(1, 2, 3)));

// Retrieve the list and add an element
List<Integer> list = map.get("numbers");
list.add(4);

Thus, HashMap does not store lists in a special way, it simply associates a key with a list object. Managing the contents of the list is done separately, through the list's own methods.