The document discusses Java collection framework. It defines a collection as a data structure capable of storing heterogeneous objects. There are three main types of collections - sets, lists, and maps. Sets cannot contain duplicate elements, lists allow duplicates and positional access, and maps store elements as key-value pairs. The core interfaces provided by the collection framework are Collection, Set, List, and Map. Common implementations of these interfaces include ArrayList, LinkedList, HashSet, TreeSet, HashMap and TreeMap. The document also covers traversing collections using iterators and list iterators, as well as examples of using sets, lists and maps.

1. Core Java
Debasish Pratihari
Collection:

A collection is a generic term for any object that
represents a set of objects grouped together by
some means or mechanism inside the memory.

Collection Framework is a specification by which
we can store and manage objects of
heterogeneous kinds in memory.

 Collection Classes
are also called
Container classes
We can define collection as a java data structure
capable of storing & managing different kinds of
objects.

Note :
A collection has a capacity to grow dynamically.
Collection Framework Provides:

Interface

Implementation

Algorithms
Core Interfaces :
Collection
Set
List
Map
SortedMap
Queue
SortedSet
Lecture/core/collection/24
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2. Core Java
Debasish Pratihari
Types of Collection:

The way a collection (group of objects) is
implemented in memory, accordingly it is
categorized into following categories.
 Set
 List
 Map
Traversing Collections:

The Followings are the ways to traverse a
collection:




For-each loop
Iterator
ListItetor
Using Methods taking index as
Parameter
Collection Interfaces and Classes :
Interface Implementation
HashSet
Set
TreeSet
ArrayList
List
LinkedList
HashMap
Map
TreeMap
Lecture/core/collection/24
Historical
Vector
Stack
Hashtable
Properties
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3. Core Java
Debasish Pratihari
Collection Interface:
Methods
public
public
public
public
public
public
public
public
public









Iterator iterator ()
boolean add (Object obj)
boolean addAll (Collection other)
boolean remove (Object obj)
void clear( )
boolean isEmpty ( )
boolean contains (Object obj)
boolean containsAll (collection other)
int size ( )
Iterator interface :

Used for traverse a Collection in forward
direction.
Methods




public
public
public
public
boolean hasNext( )
Object next( )
Object next( )
Object remove ( )
ListIterator interface :

ListIterator interface in extended from Iterator
interface.
 In contrast to Iterator interface ListIterator
interface is used to traverse a collection in
forward or backward.
Method




public
public
public
public
Object next( )
 public boolean hasPrevious( )
boolean hasNext( )  public Object remove( )
Object remove( )
 public boolean add(Object obj)
Object previous( )  public boolean set(Object obj)
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4. Core Java
Debasish Pratihari
List Interface
Methods






public
public
public
public
public
public
ListIterator listIterator( )
void add(int index, Object obj)
void addAll(int i, Collection list)
Object remove(int indx)
Object set(int indx, Object obj)
int indexOf (Object obj)
Using Set :
25% 
Support basic operation of Collection Interface

Can’t contain duplicate elements.

Implementations



HasSet
TreeSet
LinkedHashSet
Example :
import java.util.*;
class SetDemo{
public static void main(String args[]){
HashSet <String>set= new HashSet<String>();
set.add("one");
set.add("two");
set.add("three");
set.add("four");
set.add("five");
System.out.println(set);
}
}
Lecture/core/collection/24
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5. Core Java
Debasish Pratihari
Using List :

Supports basic operations of Collection
Interface.

Facilitate positional access and Searching.

Supports range operation.

Implementations:


ArrayList
LinkedList
Example:
import java.util.*;
class ListDemo{
public static void main(String args[]){
LinkedList<Integer> list= new LinkedList<Integer>();
list.add(10);
list.add(20);
list.add(30);
System.out.println(list);
ListIterator itr= list.listIterator();
while(itr.hasNext())
System.out.println(itr.next());
while(itr.hasPrevious())
System.out.println(itr.previous());
}
}
Lecture/core/collection/24
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6. Core Java
Debasish Pratihari
Using Map :

Elements are stored as key-value pair

A map can’t contain duplicate keys

Accept null as key value.

Implementations:



HashMap
TreeMap
LinkedHashMap
Example :
import java.util.*;
class MapDemo{
public static void main(String args[]){
HashMap<String,String> map
= new HashMap<String,String>();
map.put("one","java");
map.put("two","j2ee");
map.put("three","struts");
map.put("four","hibernate");
map.put("","EJB");
System.out.println(map);
}
}
HashTable vs HashMap :
HashTable
 Synchronized
 Doesn’t accept null
 Order is maintained
Lecture/core/collection/24
vs
HashMap



Un-synchronized
Accept null
No guarantee of
order
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