The Collections framework provides reusable, high-performance data structures: List (ordered, duplicates allowed), Set (unique values only), Queue (FIFO), and Map (key-value pairs). It is built on interfaces to allow interchangeable implementations (e.g., ArrayList vs LinkedList both implement List). Understanding the performance characteristics of each is crucial for interview questions.
List: A queue of customers (order matters). Set: A group of VIP members (no duplicates, order doesn't matter). Map: A phone book (names map to numbers).
You need to store a list of unique employee IDs and frequently check if a specific ID exists. List the performance characteristics of ArrayList vs HashSet for this scenario.