Collection Framework in java

COLLECTION
FRAMEWORK
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COLLECTION
FRAMEWORK
The collections framework is a unified architecture for
representing and manipulating collections, enabling
them to be manipulated independently of the details
of their representation. It reduces programming effort
while increasing performance. It enables
interoperability among unrelated APIs, reduces effort
in designing and learning new APIs, and fosters
software reuse. The framework is based on more than
a dozen collection interfaces. It includes
implementations of these interfaces and algorithms to
manipulate them.

CONTENTS
 What is Collection?
 Collections Framework
 Collections Hierarchy
 Collections Implementations
Set
List
Map

OBJECTIVES
 Define a collection
 Describe the collections framework
 Describe the collections hierarchy
 Demonstrate each collection implementation

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.

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
1. Implementations
 Concrete classes of the core interfaces providing data structures
1. Operations
 Methods that perform various operations on collections

INTERFACES
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

IMPLEMENTATIONS
Set List Map
HashSet ArrayList HashMap
LinkedHashSet LinkedList LinkedHashMap
TreeSet Vector Hashtable
Tree Map
Note: Hashtable uses a lower-case “t”

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

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

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 <variable> = <CollectionObject>.iterator();

COLLECTIONS HIERARCHY
SET AND LIST
HashSet
Collection
SortedSet
ListSet
LinkedHashSet TreeSet LinkedList Vector ArrayList
implements
implements
implements
implements extends
extends

COLLECTIONS HIERARCHY
MAP
Map
SortedMap
Hashtable
LinkedHashMap
HashMap TreeMap
implements
implements
extends
extends

COLLECTION IMPLEMENTATIONS
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)

LIST
A List cares about the index.
“Paul”“Paul” “Mark”“Mark” “John”“John” “Paul”“Paul” “Luke”“Luke”value
index 0 1 2 3 4
LinkedListLinkedListVectorVectorArrayListArrayList

LIST IMPLEMENTATIONS
ARRAY LIST
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));
}
}
One
Two
Three

VECTOR
import java.util.Vector;
public class MyVector {
Vector vecky = new Vector( );
vecky.add(new Integer(1));
for(int x=0; x<3; x++) {
System.out.println(vecky.get(x));
}
}
}
1
2
3

LINKED LIST
import java.util.LinkedList;
public class MyLinkedList {
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]);
}
}
}
1.0
2.0
3.0

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

SET IMPLEMENTATIONS
HASH SET
import java.util.*;
public class MyHashSet {
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

SET IMPLEMENTATIONS
LINKED HASH SET
import java.util.LinkedHashSet;
public class MyLinkedHashSet {
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]);
}
}
}
One
Two
Three

SET IMPLEMENTATIONS
TREE SET
import java.util.TreeSet;
import java.util.Iterator;
public class MyTreeSet {
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

MAP
A Map cares about unique identifiers.
“Paul”“Paul” “Mark”“Mark” “John”“John” “Paul”“Paul” “Luke”“Luke”
key
value
“Pl” “Ma” “Jn” “ul” “Le”
LinkedHashMapLinkedHashMap TreeMapTreeMapHashtableHashtableHashMapHashMap

MAP IMPLEMENTATIONS
HASH MAP
import java.util.HashMap;
public class MyHashMap {
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

MAP IMPLEMENTATIONS
HASH TABLE
import java.util.Hashtable;
public class MyHashtable {
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:
{address=Manila, name=Jody, id=1001}

MAP IMPLEMENTATIONS
LINKED HASH MAP
import java.util.*;
public class MyLinkedHashMap {
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()) {
}
}
}
Jody
446
Manila
Savings

MAP IMPLEMENTATIONS
TREE MAPimport 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()) {
}
}
}
Printing the VALUES....
Manila
446
Jody

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
NoNoXHashSet
NoBy insertion order or
last access order
XLinkedHashMap
By natural order or
custom comparison rules
SortedXTreeMap
NoNoXHashtable
NoNoXHashMap
SortedOrderedListSetMapClass

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.

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Landmark: Near Rohini East Metro Station, Opposite
Metro Pillar No-397
Telephone: 011-65164822
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Collection Framework in java

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