Tell me about Java collections, which ones you've worked with, and which are suitable for different tasks.

In Java, there are several main collections I have worked with:

• List (ArrayList, LinkedList) — an ordered set of elements. ArrayList is suitable for quick access by index, LinkedList for frequent insertions/deletions in the middle.
• Set (HashSet, TreeSet) — a collection of unique elements. HashSet provides fast search, TreeSet stores elements in sorted order.
• Map (HashMap, TreeMap, LinkedHashMap) — stores key-value pairs. HashMap offers quick access without order, TreeMap is sorted by key, LinkedHashMap preserves insertion order.

The choice of collection depends on the task:

• For storing unique elements without order — HashSet.
• For an ordered list with quick access — ArrayList.
• For a map with fast key-based search — HashMap.
• For sorted data — TreeSet or TreeMap.

Example of using HashMap:

Map<String, Integer> wordCount = new HashMap<>();
wordCount.put("apple", 3);
wordCount.put("banana", 2);
int count = wordCount.getOrDefault("apple", 0);