13 Collections Framework

2 Contents What is Collection? Collections Framework Collections Hierarchy Collections Implementations Set List Map

3 Objectives Define a collection Describe the collections framework Describe the collections hierarchy Demonstrate each collection implementation

4 What is a Collection? A Collection (also known as container) is an object that contains a group of objects treated as a single unit. Any type of objects can be stored, retrieved and manipulated as elements of collections.

5 Collections Framework Collections Framework is a unified architecture for managing collections Main Parts of Collections Framework 1.Interfaces Core interfaces defining common functionality exhibited by collections 2.Implementations Concrete classes of the core interfaces providing data structures 3.Operations Methods that perform various operations on collections

6 Collections Framework Interfaces Core InterfaceDescription Collection specifies contract that all collections should implement Set defines functionality for a set of unique elements SortedSet defines functionality for a set where elements are sorted List defines functionality for an ordered list of non- unique elements Map defines functionality for mapping of unique keys to values SortedMap defines functionality for a map where its keys are sorted

7 Collections Framework Implementations SetListMap HashSetArrayListHashMap LinkedHashSetLinkedListLinkedHashMap TreeSetVectorHashtable TreeMap Note: Hashtable uses a lower-case “t”

8 Collections Framework Operations Basic collection operations: Check if collection is empty Check if an object exists in collection. Retrieve an object from collection Add object to collection Remove object from collection Iterate collection and inspect each object Each operation has a corresponding method implementation for each collection type

9 Collections Characteristics Ordered Elements are stored and accessed in a specific order Sorted Elements are stored and accessed in a sorted order Indexed Elements can be accessed using an index Unique Collection does not allow duplicates

10 Iterator An iterator is an object used to mark a position in a collection of data and to move from item to item within the collection Syntax: Iterator =.iterator();

11 Collections Hierarchy Set and List HashSet Collection SortedSet List Set LinkedHashSetTreeSet LinkedList Vector ArrayList implements extends

12 Collections Hierarchy Map Map SortedMap Hashtable LinkedHashMap HashMap TreeMap implements extends

13 Set: Unique things (classes that implement Set) Map: Things with a unique ID (classes that implement Map) List: Lists of things (classes that implement List) Collection Implementations Next!

14 A List cares about the index. List “Paul” “Mark” “John” “Paul” “Luke” value index LinkedListVectorArrayList

15 List Implementations ArrayList import java.util.ArrayList; public class MyArrayList { public static void main(String args[ ]) { ArrayList alist = new ArrayList( ); alist.add(new String("One")); alist.add(new String("Two")); alist.add(new String("Three")); System.out.println(alist.get(0)); System.out.println(alist.get(1)); System.out.println(alist.get(2)); } Back! One Two Three

16 List Implementations Vector import java.util.Vector; public class MyVector { public static void main(String args[ ]) { Vector vecky = new Vector( ); vecky.add(new Integer(1)); vecky.add(new Integer(2)); vecky.add(new Integer(3)); for(int x=0; x<3; x++) { System.out.println(vecky.get(x)); } Back!

17 List Implementations LinkedList import java.util.LinkedList; public class MyLinkedList { public static void main(String args[ ]) { LinkedList link = new LinkedList( ); link.add(new Double(2.0)); link.addLast(new Double(3.0)); link.addFirst(new Double(1.0)); Object array[ ] = link.toArray( ); for(int x=0; x<3; x++) { System.out.println(array[x]); } Back!

18 A Set cares about uniqueness, it doesn’t allow duplicates. Set “Paul” “Mark” “John” “Luke” “Fred” “Peter” TreeSetLinkedHashSetHashSet

19 Set Implementations HashSet import java.util.*; public class MyHashSet { public static void main(String args[ ]) { HashSet hash = new HashSet( ); hash.add("a"); hash.add("b"); hash.add("c"); hash.add("d"); Iterator iterator = hash.iterator( ); while(iterator.hasNext( )) { System.out.println(iterator.next( )); } Back! dacbdacb

20 Set Implementations LinkedHashSet import java.util.LinkedHashSet; public class MyLinkedHashSet { public static void main(String args[ ]) { LinkedHashSet lhs = new LinkedHashSet(); lhs.add(new String("One")); lhs.add(new String("Two")); lhs.add(new String("Three")); Object array[] = lhs.toArray( ); for(int x=0; x<3; x++) { System.out.println(array[x]); } Back! One Two Three

21 Set Implementations TreeSet import java.util.TreeSet; import java.util.Iterator; public class MyTreeSet { public static void main(String args[ ]) { TreeSet tree = new TreeSet(); tree.add("Jody"); tree.add("Remiel"); tree.add("Reggie"); tree.add("Philippe"); Iterator iterator = tree.iterator( ); while(iterator.hasNext( )) { System.out.println(iterator.next( ).toString( )); } Back! Jody Philippe Reggie Remiel

22 A Map cares about unique identifiers. Map “Paul” “Mark” “John” “Paul” “Luke” key value “Pl” “Ma” “Jn” “ul” “Le” LinkedHashMapTreeMapHashtable HashMap

23 Map Implementations HashMap import java.util.HashMap; public class MyHashMap { public static void main(String args[ ]) { HashMap map = new HashMap( ); map.put("name", "Jody"); map.put("id", new Integer(446)); map.put("address", "Manila"); System.out.println("Name: " + map.get("name")); System.out.println("ID: " + map.get("id")); System.out.println("Address: " + map.get("address")); } Back! Name: Jody ID: 446 Address: Manila

24 Map Implementations Hashtable import java.util.Hashtable; public class MyHashtable { public static void main(String args[ ]) { Hashtable table = new Hashtable( ); table.put("name", "Jody"); table.put("id", new Integer(1001)); table.put("address", new String("Manila")); System.out.println("Table of Contents:" + table); } Back! Table of Contents: {address=Manila, name=Jody, id=1001}

25 Map Implementations LinkedHashMap import java.util.*; public class MyLinkedHashMap { public static void main(String args[ ]) { int iNum = 0; LinkedHashMap myMap = new LinkedHashMap( ); myMap.put("name", "Jody"); myMap.put("id", new Integer(446)); myMap.put("address", "Manila"); myMap.put("type", "Savings"); Collection values = myMap.values( ); Iterator iterator = values.iterator( ); while(iterator.hasNext()) { System.out.println(iterator.next( )); } Back! Jody 446 Manila Savings

26 Map Implementations TreeMap import java.util.*; public class MyTreeMap { public static void main(String args[]) { TreeMap treeMap = new TreeMap( ); treeMap.put("name", "Jody"); treeMap.put("id", new Integer(446)); treeMap.put("address", "Manila"); Collection values = treeMap.values() Iterator iterator = values.iterator( ); System.out.println("Printing the VALUES...."); while (iterator.hasNext()) { System.out.println(iterator.next( )); } Back! Printing the VALUES.... Manila 446 Jody

27 Collection Classes Summary NoBy indexXLinkedList NoBy indexXVector NoBy indexXArrayList NoBy insertion order or last access order XLinkedHashSet By natural order or custom comparison rules SortedXTreeSet No XHashSet NoBy insertion order or last access order XLinkedHashMap By natural order or custom comparison rules SortedXTreeMap No XHashtable No XHashMap SortedOrderedListSetMapClass

28 Key Points Collections Framework contains: 1.Interfaces 2.Implementations 3.Operations A list cares about the index. A set cares about uniqueness, it does not allow duplicates. A map cares about unique identifiers.