Different Types Of Cursor In java - NTSEQ:- A IT Infrastructure and Cyber Security Blogs

If we want to get objects one by one from the collection we should go for cursor.
There are 3 type of cursors available in java
Enumeration
Iterator
List Iterator

Enumeration:-

It is a cursor to retrieve objects one by one from the collection
It is applicable for legacy classes
We can create Enumeration object by using elements()

Public Enumeration elements();

Eg: Enumeration e = v.elements();

where v is a Vector Object

Enumeration Interface define the following two methods:

Public Boolean has MoreElements();
Public Object nextElement();

Example:-

import java.util.*;
class Enumeration_Demo
{
public static void main(String[] args)
{
Vector v=new Vector();
for(int j=0;j<=10;j++)
{
v.addElement(j);
}

Enumeration e=v.elements();
System.out.println("Even numbers are :-");
while(e.hasMoreElements())
{
Integer k=(Integer)e.nextElement();
if(k%2==0)
System.out.println(k);
}
System.out.print("vector elements are :-" + v);
}
}

Output:-

Limitation of Enumeration are below:-

Enumeration concept is applicable only for legacy classes & hence it is not universal cursor.
By using Enumeration we van get only Read Access & we cant perform any remove operations.
To over come these limitations sun people introduced Iterator in 1.2 verson.

2. Iterator:

We can apply Iterator concept for any collection object. It is a universal cursor.
While Iterating we can perform remove operation also in addition to read operation.
We can use Iterator to get objects one by one from any collection object.
We can get Iterator object by Iterator() of collection interface.

Iterator itr = C.iterator()

Iterator Interface defines the following 3 methods :

public Boolean hasNext();
public Object next();
public void remove();

Example:-

import java.util.*;

class Iterator_Demo
{
public static void main(String[] args)
{
ArrayList al=new ArrayList();
for(int j=0;j<=10;j++)
{
al.add(j);
}

System.out.println(al);
Iterator itr=al.iterator();
while(itr.hasNext())
{
Integer k=(Integer)itr.next();
if(k%2==0)
System.out.println(k);
else
itr.remove();
}
System.out.println(al);
}
}

Limitations of Iterator:

Both enumeration and Iterator are single direction cursors only that’s why we can always move only forward direction and we can’t move to the backward direction.
While iterating by Iterator we can perform only read and remove operations and we can’t perform replacement and addition of new objects.
To overcome these limitations sun people introduced list-iterator concept.

3. ListIterator:-

ListIterator is the child interface of Iterator.
By using listIterator we can move either to the forward direction (or) to the backward direction that is it is a bi-directional cursor.
While iterating by listIterator we can perform replacement and addition of new objects in addition to read and remove operations
By using listIterator method we can create listIterator object.

ListIterator itr=l.listiterator();

ListIterator interface supports following 9 methods

1) public boolean hasNext(); forward
2) public Object next(); forward
3) publicintnextIndex(); forward
4) publicbooleanhasPrevious(); backward
5) public Object previous(); backward
6) publicintpreviousIndex(); backward
7) public void remove();
8) public void set(Object o);
9) public void add(Object new);

Example:-

import java.util.*;
class ListIterator_Demo
{
public static void main(String[] args)
{
LinkedList L=new LinkedList();
L.add("A");
L.add("B");
L.add("c");
L.add("D");
System.out.println(L);
ListIterator ltr=L.listIterator();
while(ltr.hasNext())
{
String s=(String)ltr.next();
if(s.equals("A"))
{
ltr.remove();
}
}
System.out.println(L);
}
}

Note:- listIterator is the most powerful cursor but it’s limitation is only applicable for “List objects”.

Leave a Reply Cancel reply