Question

Need help completing my instance method for deleteFront() as specified below

To the class IntegerLinkedList, add an instance method deleteFront such that …

• Method deleteFront has no input.
• Method deleteFront returns …
  • an empty Optional instance if the list is empty
  • an Optional instance whose value is the integer that was deleted from the front of the list, otherwise

Hints

• https://docs.oracle.com/javase/10/docs/api/java/util/Optional.html

import java.util.Optional;

    public class IntegerLinkedList
    {

        private IntegerNode head ;
        private int numberOfItems ;

        public int getNumberOfItems() { return numberOfItems; }

        public IntegerLinkedList() { head = null; numberOfItems = 0; }

        @Override
        public String toString()
        {
            String returnString = "[" ;
            IntegerNode node = head ;
            for ( int i = 0; i < numberOfItems; i ++ )
            {
                returnString +=  ( i == 0 ? "" : "," ) ;
                returnString += node.getData() ;
                node = node.getNext() ;
            }
            returnString += "]" ;
            return returnString ;
        } // end toString

        public void insertFront(int a)
        {
            IntegerNode nodeA = new IntegerNode(a);
            nodeA.setNext(head);
            head = nodeA;
            numberOfItems++;
        }

        public Optional deleteFront()
        {
            Optional opt = Optional.empty();
            if(head == null)
            {

            }
            else
            {
                IntegerNode temp = head.getNext();
                head = temp;

            }
            return opt;
        }
    } // end IntegerLinkedList

public class IntegerNode
{
private int data;
private IntegerNode next;
public IntegerNode () { data = 0; next = null; }
public IntegerNode ( int data ) { setData( data ); next = null; }
public int getData () { return data; }
public IntegerNode getNext () { return next; }
public IntegerNode setData ( int data ) { this.data = data; return this; }
public IntegerNode setNext( IntegerNode next ) { this.next = next; return this; }
}

Answer 1

//Everything remains same except the deleteFront function , so I am posting this function , Please make this changes to IntegerLinkedList.java file

public Optional deleteFront()

{

Optional opt = Optional.empty();

if(head == null)

{

return opt;

}

else

{

IntegerNode temp = head.getNext();

opt=Optional.of(head.getData());

head = temp;

}

return opt;

}

===========================

//I am providing Main.java method to test the code

class Main {

public static void main(String[] args) {

//System.out.println("Hello world!");

IntegerLinkedList list=new IntegerLinkedList();

list.insertFront(1);

list.insertFront(2);

list.insertFront(3);

list.insertFront(4);

list.insertFront(5);

System.out.println("Integer list contant: ");

System.out.println(list);

//Testing if deleteFront returns values when not empty otherwise prints empty

System.out.println("Testing deleteFront function");

System.out.println(list.deleteFront());

System.out.println(list.deleteFront());

System.out.println(list.deleteFront());

System.out.println(list.deleteFront());

System.out.println(list.deleteFront());

System.out.println(list.deleteFront());

}

}

=================================

//Output

Integer list contant:
[5,4,3,2,1]
Testing deleteFront function
Optional[5]
Optional[4]
Optional[3]
Optional[2]
Optional[1]
Optional.empty