- ConcurrentHashMap -- High performance thread-aware map. A simple test which inserts 10000 Integer for each threads shows that:
Type No of threads Average Time (sec) ConcurrentHashMap 2 0.06 Synchronized HashMap 2 0.06 ConcurrentHashMap 10 0.18 Synchronized HashMap 10 0.59 ConcurrentHashMap 20 0.25 Synchronized HashMap 20 1.15
more thread, more performance gain
- CopyOnWriteArrayList, CopyOnWriteArraySet -- A thread-aware List/Set optimize for read. DO NOT use these for a lots of write operations !
- Choose the right collection:
Auto-Sorted Random write Random read Maintain
Note ArrayList X X OK for < 1000 O O choose this first PriorityQueue X O X X X Not allow null LinkedList X X O (fast sort) poor O (Queue) allow null HashMap O (key) X O O X WeakHashMap for cache TreeMap O (key) O O O X with Comparator LinkedHashMap O (key) X O O O HashSet O X X X X TreeSet O O X X X with Comparator LinkedHashSet O X X X O
- Never use Vector, Stack, and Hashtable.
To be continue...