XiaoLinCoding Java Interview Guide

Redis provides several data types categorized into basic and advanced types. Each is suited for specific use cases:

Basic Types:

• String: Caching objects, general counters, distributed locks, shared session information.
• List: Message queues (though requires manual unique ID implementation and lacks consumer group support).
• Hash: Caching objects, shopping carts.
• Set: Aggregate calculations (unions, intersections, differences), likes, common followers, lottery activities.
• ZSet (Sorted Set): Ranking scenarios, leaderboards, sorting by name/phone.

Advanced Types:

• BitMap (v2.2+): Binary state statistics, sign-in tracking, login status, continuous sign-in counts.
• HyperLogLog (v2.8+): Cardinality estimation for massive datasets, e.g., million-level page UV counting.
• GEO (v3.2+): Geographic location storage, e.g., ride-hailing services.
• Stream (v5.0+): Advanced message queues with automatic global unique message IDs and consumer group support.

The Java Collection Framework is organized into two main hierarchies: the Collection interface (single-column collections) and the Map interface (key-value pairs).

Collection Hierarchy:

• List: Ordered, allows duplicates. Implementations include ArrayList (dynamic array, fast random access), LinkedList (doubly-linked list, fast insert/delete), and Vector (thread-safe array).
• Set: Unordered, no duplicates. Implementations include HashSet (backed by HashMap), LinkedHashSet (maintains insertion order), and TreeSet (sorted via TreeMap).
• Queue: First-in-first-out (FIFO). LinkedList implements this interface.

Map Hierarchy:

• HashMap: Array + Linked List. In JDK 1.8+, converts lists to Red-Black Trees when length exceeds 8 to optimize search time.
• LinkedHashMap: Extends HashMap with a doubly-linked list to maintain insertion or access order.
• TreeMap: Implemented as a Red-Black Tree for sorted keys.
• ConcurrentHashMap: Thread-safe implementation using volatile, CAS, and synchronized (JDK 1.8+).