collections in JDK

Transcript

1. collections in JDK - basic data structures you should know - 2012/Aug/29 Kengo TODA
2. Basic collection List<T> Set<T> Map<K, T>
3. ArrayList<T> It just wraps an array Good to #get(int): O(1) Bad to #remove(int), #contains(T) : O(n)
4. LinkedList<T> 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)
5. How to choose? ArrayList: Stack When we needs random access LinkedList: Stack, Queue (java.util.Deque) When we treat head or tail frequently
6. HashMap<K, V> It use hash table to manage key We have to implement #hashCode() correctly It does not implement SortedMap interface
7. TreeMap<K, V> It use red-black tree to manage key We have to implement Comparable or Comparator correctly It implements SortedMap
8. LinkedHashMap<K, V> A subclass of HashMap It has bidirectional list to memory insertion- order (or access-order) It does not implement SortedMap interface
9. How to choose? HashMap Standard use TreeMap When we have to use ordering LinkedHashMap When we have to memory insertion-order
10. Set ≒ Map HashSet → HashMap TreeSet → TreeMap LinkedHashSet → LinkedHashMap
11. Legacy implementations Vector Stack Hashtable Properties ＠Deprecated
12. Additional collection Google guava contains useful collections Table<C, R, V> Multiset<T> Multimap<K, V>
13. References Source code (OpenJDK, Google guava)