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MELJUN CORTES Java Lecture Collections
MELJUN CORTES Java Lecture Collections
MELJUN CORTES Java Lecture Collections
MELJUN CORTES Java Lecture Collections
MELJUN CORTES Java Lecture Collections
MELJUN CORTES Java Lecture Collections
MELJUN CORTES Java Lecture Collections
MELJUN CORTES Java Lecture Collections
MELJUN CORTES Java Lecture Collections
MELJUN CORTES Java Lecture Collections
MELJUN CORTES Java Lecture Collections
MELJUN CORTES Java Lecture Collections
MELJUN CORTES Java Lecture Collections
MELJUN CORTES Java Lecture Collections
MELJUN CORTES Java Lecture Collections
MELJUN CORTES Java Lecture Collections
MELJUN CORTES Java Lecture Collections
MELJUN CORTES Java Lecture Collections
MELJUN CORTES Java Lecture Collections
MELJUN CORTES Java Lecture Collections
MELJUN CORTES Java Lecture Collections
MELJUN CORTES Java Lecture Collections
MELJUN CORTES Java Lecture Collections
MELJUN CORTES Java Lecture Collections
MELJUN CORTES Java Lecture Collections
MELJUN CORTES Java Lecture Collections
MELJUN CORTES Java Lecture Collections
MELJUN CORTES Java Lecture Collections
MELJUN CORTES Java Lecture Collections
MELJUN CORTES Java Lecture Collections
MELJUN CORTES Java Lecture Collections
MELJUN CORTES Java Lecture Collections
MELJUN CORTES Java Lecture Collections
MELJUN CORTES Java Lecture Collections
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MELJUN CORTES Java Lecture Collections

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MELJUN CORTES Java Lecture Collections

MELJUN CORTES Java Lecture Collections

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  • *not sure how small “small” is… hundreds?
  • Transcript

    • 1. The Collections Framework MELJUN CORTES Java Data Structures MELJUN CORTES
    • 2. What You Should Learn  Definition  Types of Collections  Using Collections Iterating  Copying  Collections in Java 1.5 
    • 3. Definition Collection  object that groups multiple elements into a single unit  an array is a collection
    • 4. Definition Collections Framework  unified architecture for representing and manipulating collections
    • 5. Definition Collections Framework  Three Elements:  Interfaces   Implementations   how you handle the collection the classes that actually hold the data Algorithms  useful routines
    • 6. The Java Collections Framework  Interfaces Collection List Set Queue Map
    • 7. The Java Collections Framework  Collection  super type of List, Set and Queue  List  stores elements in the order they were added, similar to an array only growable  Set  stores only unique elements, no duplicates  Queue  stores elements in preparation for processing, usually either by FIFO or by priority  Map  stores key-value pairs, like for a lookup table
    • 8. Collection  Defines common methods      add addAll remove removeAll clear       contains containsAll isEmpty size toArray iterator
    • 9. Lists  “growable array”  Elements ordered in the sequence they were added.  Allows you to get and set using and index myList.set(4, “Barracuda”); String fish = myList.get(4);
    • 10. Lists Implementations:  ArrayList  LinkedList  Vector
    • 11. Lists ArrayList  backed by an Object array  fast in getting and setting elements  slow in inserting and removing
    • 12. Lists LinkedList  slow in getting and setting elements  fast in inserting and removing
    • 13. Lists Vector  Just like an ArrayList only all methods are synchronized.  Was the only list available prior to Java 1.1.  ArrayList is preferred to Vector because programmer has control over synchronization.
    • 14. Sets  No duplicates  Maintains its own order  Same interface as Collection
    • 15. Sets Implementations:  HashSet  TreeSet
    • 16. Sets  HashSet  Stores data in a hash table implementation.  Not sorted “naturally”.
    • 17. Sets  TreeSet  Stores data in a binary tree to search for duplicates.  Sorted “naturally”  Implements SortedSet interface
    • 18. Queues  For holding elements prior to processing.  Typically FIFO but may be ordered by priority  Implementations: LinkedList (FIFO)  PriorityQueue 
    • 19. Queues  Methods element  offer  Peek  poll  remove 
    • 20. Maps  An object that maps keys to values  Keys are unique Key (User ID – String) “C234D7” “A497X3” “B252M5” “R567B7” Value (some object)
    • 21. Maps  Using a map: myMap.put(“T234Y9”, someObject);  Getting from a map: myMap.get(“T234Y9”);
    • 22. Maps Implementations:  HashMap  TreeMap  HashTable
    • 23. Maps  HashMap Keys are ordered using a hash table implementation, similar to HashSet.  Keys are not sorted “naturally”. 
    • 24. Maps  TreeMap Uses a binary tree to order keys.  Keys are sorted “naturally”. 
    • 25. Maps  HashTable Just like an HashMap only all methods are synchronized.  Was the only map available prior to Java 1.1.  HashMap is preferred to HashTable because programmer has control over synchronization. 
    • 26. Maps  HashMap vs. TreeMap HashMap is usually faster than TreeMap.  Use TreeMap if you need keys to be sorted. 
    • 27. Iterator  Prior to Java 1.5, Iterator was used to provide generic iteration for Collection implementations.
    • 28. Iterator //example: collection of strings Iterator iter = collection.iterator(); while(iter.hasNext) { String s = (String) iter.next(); // do stuff with s }
    • 29. Algorithms  java.util.Collections  Utility class where useful routines can be found.       Sorting Searching Finding Maximum, Minimum Reversing Shuffling more...
    • 30. Java 1.5 Enhancements  Generics  For-Each Loop  Autoboxing
    • 31. Generics  You can enforce type on the collection. List<String> list = new ArrayList<String>(); String s = list.get(5); // no need to cast! list.add(new Integer(5)); XXX // will not compile
    • 32. For-Each Loop  Use the same loop construct for arrays and collections: for(String s : collection) { System.out.println(s); }
    • 33. Autoboxing  You can now use primitives in Collections list.add(3); map.put(4857, employee);
    • 34. Best Practices  Always use the Interface.  Always use the Iterator (1.4) or the For- Each Loop (1.5).

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