24/03/25
-----------
                                Cursors in Java Collection Framework
				-----------------------------------------
Q)What is a cursor?
=>A cursor is an iterator used to traverse a collection.

Note:- Traversing referes to the process of visiting and accessing each element
of a data structure.

Q)What are the different types of cursors in Java collection framework?
 =>There are 4 types of cursors.
         1)Enumeration
	 2)Iterator
	 3)ListIterator
	 4)Spliterator
Q)Explain about Enumeration.
=>java.util.Enumeration interface provides methods using which we can enumerate(obtain one by one) the elements of the collection.
=>This legacy cursor was used in legacy collections for eg. Vector, Stack etc.
=>This interface has 3 methods.
          1)hasMoreElements()
	  2)nextElement()
          3)default  Iterator<E> asIterator() (used to convert Enumeration into Iterator)
Q)What are the limitations of Enumeration?
1)can be used for read-only operations
2)unidirectional traversing
3)performance problem for read operation also

Q)Explain about Iterator.
  =>java.util.Iterator is an interface.
  =>It is known as a universal cursor.I.e. it can be used to iterate any collection(list based,set based or map based).
 =>It is a unidirectional cursor. I.e. it can traverse the elements of collection in forward direction only.
 =>We can perform  two kinds of operations only on the collection using Iterator.
             1)reading of elements of the collection
	     2)removing the elements of the collection
=>Iterator has the following methods.
          1)boolean hasNext()
	  2)E  next()
	  3)void remove()
	  4)void forEachRemaining(lambda expression)
Q)Example program on Iterator.

Q)What are the limitations of Iterator?
import java.util.*;
class  IteratorExample{
	public static void main(String[] args){
		ArrayList<Integer> list=new ArrayList<>();
		Collections.addAll(list,10,20,25,30,35);
		Iterator<Integer> iterator1=list.iterator();
		Iterator<Integer> iterator2=list.iterator();//to traverse again
                System.out.print("Numbers in the list:");
		iterator1.forEachRemaining(n->System.out.print(n+" "));

		while(iterator2.hasNext()){
			if(iterator2.next() % 2==0){
				iterator2.remove();
			}
		}
		System.out.println();
		System.out.print("Numbers in the list after removal:");
		for(int n:list)
		   System.out.print(n+" ");
	}
}
Q)What are the limitations of Iterator?
1)traverses the collection only in forward direction
2)All CRUD operations can't be perfroming on collection.
 I.e. read and remove only allowed

Note:- ListIterator overcomes the limitations of Iterator.

Q)Explain about ListIterator.
=>java.util.ListIterator is the sub interface of Iterator.

=>by calling listIterator() method on the list based collection object,
ListIterator object can be created.

=>It is a bidirectional cursor. I.e. using this cursor, we can traverse the list based
collection in forward and backward direction.

=>It can be used only with list based collections.

=>Using ListIterator, all CRUD oeprations can be performed on the collection

Q)Example program on ListIterator.
import java.util.*;
class  ListIteratorExample{
	public static void main(String[] args){
		ArrayList<Integer> list=new ArrayList<>();
		Collections.addAll(list,10,20,30,40);
		ListIterator<Integer> li=list.listIterator();
		System.out.print("Elements of the list:");
		while(li.hasNext()){
			System.out.print(li.next()+" ");
		}
        System.out.println();//blank line
		System.out.print("Elements of the list in backward direction:");
		while(li.hasPrevious()){
			System.out.print(li.previous()+" ");
		}
		while(li.hasNext()){
                if(li.nextIndex()==0){
			   li.set(18);//Updation
		   }
		   if(li.nextIndex()==2){
			   li.add(25);//storing data into the collection
		   }
		   li.next();
		}//while
		System.out.println();
		System.out.println(list);
	}
}