Cursors in Java

What is Cursor?

• If We want to get Objects One by One from the Collection, than we should go for Cursor.
• 3 Types of Cursor Available in Java.

1. Enumeration
2. Iterator
3. ListIterator

Enumeration

• We can Use Enumeration to get Objects One By One From Legacy Classes.
• We can create Enumeration Object By Using Elements Method of Vector Classes.

        public Enumeration elements();

 for eg:   

        Enumeration e = v.elements();

Methods

1. public boolean hasMoreElements();
2. public object nextElement();

Limitations of Enumeration(1.0v)

• We can apply Enumeration concept only for Legacy Classes and it is not Universal Cursor.
• By using Enumeration we can get only Read Access & We can't perform Remove Operation.

To Overcome Enumeration Limitations, we should go for Iterator.

Iterator(Interface)

• We can apply Iterator Concept for any Collection Object.
• It is Universal Cursor.
• By using, Iterator We can Perform Both Read & Remove Operations.
• We can create Iterator Object by using, Iterator Method of Collection Interface. 

         public Iterator iterator()

for eg:

           Iterator itr = c iterator();

Here, c is Any Collection Object.

Methods of Iterator

• public boolean hasNext();
• public Object next();
• public void remove();

Limitations of Iterator

• By using, Enumeration & Iterator we can always move only towards  Forward Direction & we can't move towards Backward direction these are Single direction cursor.
• By Using, Iterator we can perform only Read & Remove Operations we can't perform Replacement & Addition of new Object.

To Overcome Iterator Limitations we should go for ListIterator.

ListIterator(Interface)

• By Using, ListIterator we can move either to the Forward & Backward Direction.
• It is Bidirectional Cursor.
• By using ListIterator we can perform, Replacement an addition of new Object in addition to Read & Remove Operations.
• We can create ListIterator By using, ListIterator method for ListIterator Interface.

          public  ListIterator listIterator();

for eg:

        ListIterator itr = l.listIterator();

Here, l is Any List Object.

Methods Of ListIterator

• ListIterator is Child Interface of Iterator Hence, All methods present in Iterator By default, available to the ListInterface.

Forward Direction Method

• public boolean hasNext()
• public Object next()
• public int nextIndex()

Backward Direction Method

• public boolean previousNext()
• public Object previous()
• public int previousIndex()

Extra Method

• public void move()
• public void add(object o)
• public void set(object o)

Limitations of ListIterator

• The Most Powerful Cursor is ListIterator But, it is applicable only for List Objects.