collections in JDK

Transcript

1. collections in JDK
   - basic data structures you should know -
   2012/Aug/29 Kengo TODA
   

   View Slide

2. Basic collection
   List
   Set
   Map
   

   View Slide

3. ArrayList
   It just wraps an array
   Good to #get(int): O(1)
   Bad to #remove(int), #contains(T) : O(n)
   

   View Slide

4. LinkedList
   Simple bidirectional list
   It costs more Java heap than ArrayList
   Good to #remove & #add for head/tail: O(1)
   Bad to #get(int), #contains(T) : O(n)
   

   View Slide

5. How to choose?
   ArrayList:
   Stack
   When we needs random access
   LinkedList:
   Stack, Queue (java.util.Deque)
   When we treat head or tail frequently
   

   View Slide

6. HashMap
   It use hash table to manage key
   We have to implement #hashCode() correctly
   It does not implement SortedMap interface
   

   View Slide

7. TreeMap
   It use red-black tree to manage key
   We have to implement Comparable or
   Comparator correctly
   It implements SortedMap
   

   View Slide

8. LinkedHashMap
   A subclass of HashMap
   It has bidirectional list to memory insertion-
   order (or access-order)
   It does not implement SortedMap interface
   

   View Slide

9. How to choose?
   HashMap
   Standard use
   TreeMap
   When we have to use ordering
   LinkedHashMap
   When we have to memory insertion-order
   

   View Slide

10. Set ≒ Map
    HashSet → HashMap
    TreeSet → TreeMap
    LinkedHashSet → LinkedHashMap
    

    View Slide

11. Legacy implementations
    Vector
    Stack
    Hashtable
    Properties
    ＠Deprecated
    

    View Slide

12. Additional collection
    Google guava contains useful collections
    Table
    Multiset
    Multimap
    

    View Slide

13. References
    Source code (OpenJDK, Google guava)
    

    View Slide