20-03-25
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Q)What is an ArrayList?
=>java.util.ArrayList is a list based collection class.
=>ArrayList is the most widely used list based collection class.
=>It uses dynamic array(both growable and shrinkable array) as underlying
data structure.
=>It is non-synchronized.
=>ArrayList is best suited for rea-only lists.
=>ArrayList compromises performance while manipulating its elements
as the elements are to be shifted.

DIAGRAM

Q)What are the important methods of ArrayList?
 =>that of java.util.Collection  &   java.util.List  interfaces
Note:- Collection interface and List interface exampe programs are of ArrayList only.

Q)What is LinkedList?
=>LinkedList is a list based collection class.
=>Insertion order is maintained.
=>It can contain duplicate elements.
=>It is non-synchronized.
=>In the background it uses doubly linked list data structure.
=>Insertions and removals are very effcient as no shifting of elements is involved.

DIAGRAM


Q)Java program to compare the performance between ArrayList and LinkedList for rea-only operation.
import java.util.*;
class  PerformanceTest
{
	public static void main(String[] args) 
	{
		LinkedList<Integer> llist=new LinkedList<>();
		ArrayList<Integer> alist=new ArrayList<>();
		Collections.addAll(llist,1,2,3,4,5,6,7,8,9,1,2,3,4,5,6,7,8);
		Collections.addAll(alist,1,2,3,4,5,6,7,8,9,1,2,3,4,5,6,7,8);
		Iterator iterator1=llist.iterator();
		long t1=System.nanoTime();
		while(iterator1.hasNext())
			iterator1.next();
		long t2=System.nanoTime();
		long timetaken=t2-t1;
		System.out.println("Time taken to read the linked list :"+timetaken+" nano seconds");

		Iterator iterator2=alist.iterator();
		t1=System.nanoTime();
		while(iterator2.hasNext())
			iterator2.next();
		t2=System.nanoTime();
		 timetaken=t2-t1;
		System.out.println("Time taken to read the array list :"+timetaken+" nano seconds");

	}
}
Q)What are the differences between ArrayList and LinkedList?

ArrayList                                            LinkedList
******************************************************
1)underlying data structure                doubly-linked list
is resizable array.

2)elements are stored                        no
in contiguous memory
locations.

3)It is best suited                            best suited for manipulated lists
for read-only lists

4)It is an array like                         It acts  as a  list,stack
collection object                             and queue.
with API support
to deal with the elements.
******************************************************