What collections in Java do you use in automation?

In Java test automation, I often use the following collections:

• List (ArrayList, LinkedList) — for storing ordered sets of test data or steps.
• Set (HashSet, LinkedHashSet) — when it is necessary to guarantee the uniqueness of elements, for example, unique test identifiers.
• Map (HashMap, LinkedHashMap, TreeMap) — for storing key-value pairs, such as test parameters and their values.

Example of usage:

List<String> testSteps = new ArrayList<>();
testSteps.add("Open page");
testSteps.add("Login");

Set<String> uniqueUsers = new HashSet<>();
uniqueUsers.add("user1");
uniqueUsers.add("user2");

Map<String, String> testParams = new HashMap<>();
testParams.put("browser", "chrome");
testParams.put("env", "staging");

The choice of a specific collection depends on the task: whether ordering, uniqueness, quick access by key, etc., are needed.