Question

Please answer in Java. The code that needs to be modified is below. Thank you.

Question: Implement Doubly Linked List add method which add an element to a specific position. - It’s an instance method that takes a position and an element, then adds the element to this specific position and shifts the element currently at this position and any subsequent elements to the right. It throws an exception if the position is out of bound. It traverses the list from header if the position is closer to the header and traverses the list from trailer otherwise.

CODE:

class DLinkedList<E>{

private static class DNode<E>{

private E element;

private DNode<E> prev;

private DNode<E> next;

public DNode(E e){

this(e, null, null);

}

public DNode(E e, DNode<E> p, DNode<E> n){

element = e;

prev = p;

next = n;

}

public E getE(){

return element;

}

public DNode<E> getPrev(){

return prev;

}

public DNode<E> getNext(){

return next;

}

public void setE(E e){

element = e;

}

public void setPrev(DNode<E> p){

prev = p;

}

public void setNext(DNode<E> n){

next = n;

}

}

private DNode<E> header;

private DNode<E> trailer;

private int size;

public DLinkedList(){

header = new DNode<E>(null);

trailer = new DNode<E>(null, header, null);

header.setNext(trailer);

size = 0;

}

public void print(){

DNode<E> temp = header.getNext();

while (temp != trailer){

System.out.print(temp.getE().toString() + ", ");

temp = temp.getNext();

}

System.out.println();

}

}

Answer 1

class A{
   public static void main(String[] args)throws Exception {
       DLinkedList dl = new DLinkedList();
       dl.add(0,20);
       dl.add(0,25);
       dl.print();
   }
}
class DLinkedList<E>{

   private static class DNode<E>{

       private E element;

       private DNode<E> prev;

       private DNode<E> next;

       public DNode(E e){

       this(e, null, null);

       }

       public DNode(E e, DNode<E> p, DNode<E> n){

       element = e;

       prev = p;

       next = n;

       }

       public E getE(){

       return element;

       }

       public DNode<E> getPrev(){

       return prev;

       }

       public DNode<E> getNext(){

       return next;

       }

       public void setE(E e){

       element = e;

       }

       public void setPrev(DNode<E> p){

       prev = p;

       }

       public void setNext(DNode<E> n){

       next = n;

       }

   }

   private DNode header;

   private int size;

   public DLinkedList(){

   size = 0;

   }

   public void add(int index, E value) throws Exception
   {
   if(index > size || index < 0)
   {
   throw new IndexOutOfBoundsException();
   }
   if (header == null)
   {
   DNode n = new DNode(value, null, null);
   n.next = n;
   n.prev = n;
   header = n;
   }
   else
   {
   DNode current = header;
   for (int i = 0; i < index; i++)
   {
   current = current.next;
   }
   DNode n2 = new DNode(value, current, current.prev);
   current.prev.next = n2;
   current.prev = n2;
   if(index == 0)
   {
   header = n2;
   }
   }
   size++;
   }
public void print(){
   DNode current = header;
   for (int i = 0; i < size; i++)
{
   System.out.println(current.element);
current = current.next;
}
}

}

THE CHANGES ARE IN BOLD