Can you list the main data structures used in Java?

In Java, the main data structures are presented in the java.util package and include:

• List (e.g., ArrayList, LinkedList) — ordered collections that allow duplicates.
• Set (e.g., HashSet, TreeSet) — collections of unique elements.
• Map (e.g., HashMap, TreeMap) — collections of key-value pairs.
• Queue (e.g., LinkedList, PriorityQueue) — collections for organizing queues.
• Stack — a class for stack (although now Deque is more commonly used as a stack).

Each structure has its own performance characteristics and use cases. For example, ArrayList provides fast access by index, while LinkedList is convenient for frequent insertions and deletions.