13 Collections Framework

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13 Collections Framework
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Contents

• What is Collection?
• Collections Framework
• Collections Hierarchy
• Collections Implementations
• Set
• List
• Map

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Objectives

• Define a collection
• Describe the collections framework
• Describe the collections hierarchy
• Demonstrate each collection implementation

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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.

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Collections Framework

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

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Collections FrameworkInterfaces
Core Interface Description
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
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Collections FrameworkImplementations
Set List Map
HashSet ArrayList HashMap
LinkedHashSet LinkedList LinkedHashMap
TreeSet Vector Hashtable
TreeMap
Note Hashtable uses a lower-case t
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Collections FrameworkOperations

• 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

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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

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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 ltvariablegt ltCollectionObjectgt.iterator(
  )

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Collections HierarchySet and List
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Collections HierarchyMap
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Collection Implementations
List Lists of things (classes that implement
List)
Set Unique things (classes that implement Set)
Map Things with a unique ID (classes that
implement Map)
Next!
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List

• A List cares about the index.

LinkedList
Vector
ArrayList
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List ImplementationsArrayList

• 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))

One Two Three
Back!
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List ImplementationsVector

• 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 x0 xlt3 x)
• System.out.println(vecky.get(x))

1 2 3
Back!
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List ImplementationsLinkedList

• 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 x0 xlt3 x)
• System.out.println(arrayx)

1.0 2.0 3.0
Back!
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Set
John
Luke
Paul
Mark
Fred
Peter

• A Set cares about uniqueness, it doesnt allow
  duplicates.

TreeSet
LinkedHashSet
HashSet
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Set ImplementationsHashSet

• 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( ))

d a c b
Back!
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Set ImplementationsLinkedHashSet

• 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 x0 xlt3 x)
• System.out.println(arrayx)

One Two Three
Back!
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Set ImplementationsTreeSet

• 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( ))

Jody Philippe Reggie Remiel
Back!
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Map
ul
key value
Pl
Ma
Jn
Le
Mark
John
Paul
Luke
Paul

• A Map cares about unique identifiers.

LinkedHashMap
TreeMap
Hashtable
HashMap
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Map ImplementationsHashMap

• 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"))

Name Jody ID 446 Address Manila
Back!
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Map ImplementationsHashtable

• 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)

Table of Contents addressManila, nameJody,
id1001
Back!
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Map ImplementationsLinkedHashMap
Jody 446 Manila Savings

• 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!
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Map ImplementationsTreeMap

• 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( ))

Printing the VALUES.... Manila 446 Jody
Back!
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Collection Classes Summary
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Key Points

• Collections Framework contains
• Interfaces
• Implementations
• Operations
• A list cares about the index.
• A set cares about uniqueness, it does not allow
  duplicates.
• A map cares about unique identifiers.