Grocery shopping list (linked list: inserting at the end of a list) Java (SOLVED)-CodePudding

I am working on a Lab for a java class. Here are the directions and the codes given: Given main() in the ShoppingList class, define an insertAtEnd() method in the ItemNode class that adds an element to the end of a linked list. DO NOT print the dummy head node.

Ex. if the input is:

4 Kale Lettuce Carrots Peanuts where 4 is the number of items to be inserted; Kale, Lettuce, Carrots, Peanuts are the names of the items to be added at the end of the list.

The output is:

Kale Lettuce Carrots Peanuts

 public class ItemNode {
   private String item;
   private ItemNode nextNodeRef; // Reference to the next node                                        

   public ItemNode() {
      item = "";
      nextNodeRef = null;
   }

   // Constructor                                                                                     
   public ItemNode(String itemInit) {
      this.item = itemInit;
      this.nextNodeRef = null;
   }

   // Constructor                                                                                     
   public ItemNode(String itemInit, ItemNode nextLoc) {
      this.item = itemInit;
      this.nextNodeRef = nextLoc;
   }

   // Insert node after this node.                                                                   
   public void insertAfter(ItemNode nodeLoc) {
      ItemNode tmpNext;

      tmpNext = this.nextNodeRef;
      this.nextNodeRef = nodeLoc;
      nodeLoc.nextNodeRef = tmpNext;
   }

   // TODO: Define insertAtEnd() method that inserts a node
   //       to the end of the linked list  


   // Get location pointed by nextNodeRef                                                             
   public ItemNode getNext() {
      return this.nextNodeRef;
   }
   
   public void printNodeData() {
      System.out.println(this.item);
   }
}

This is also part of it, but this code can not be edited:

import java.util.Scanner;

public class ShoppingList {
   public static void main (String[] args) {
      Scanner scnr = new Scanner(System.in);

      ItemNode headNode;  // Create intNode objects                                                   
      ItemNode currNode;
      ItemNode lastNode;

      String item;
      int i;

      // Front of nodes list                                                                         
      headNode = new ItemNode();
      lastNode = headNode;

      int input = scnr.nextInt();

      for(i = 0; i < input; i   ){
         item = scnr.next();
         currNode = new ItemNode(item);
         lastNode.insertAtEnd(headNode, currNode);
         lastNode = currNode;
      }

      // Print linked list                                                                           
      currNode = headNode.getNext();
      while (currNode != null) {
         currNode.printNodeData();
         currNode = currNode.getNext();
      }
   }
}

This is what I have, but the code doesn't give the output in the correct order. Can anyone help me understand what I need to change, please?

public class ItemNode {
   private String item;
   private ItemNode nextNodeRef; // Reference to the next node                                        

   public ItemNode() {
      item = "";
      nextNodeRef = null;
   }

   // Constructor                                                                                     
   public ItemNode(String itemInit) {
      this.item = itemInit;
      this.nextNodeRef = null;
   }

   // Constructor                                                                                     
   public ItemNode(String itemInit, ItemNode nextLoc) {
      this.item = itemInit;
      this.nextNodeRef = nextLoc;
   }

   // Insert node after this node.                                                                   
   public void insertAfter(ItemNode nodeLoc) {
      ItemNode tmpNext;

      tmpNext = this.nextNodeRef;
      this.nextNodeRef = nodeLoc;
      nodeLoc.nextNodeRef = tmpNext;
   }

   // TODO: Define insertAtEnd() method that inserts a node
   //       to the end of the linked list  
   public void insertAtEnd(ItemNode headNode, ItemNode currNode){
       currNode.nextNodeRef = headNode.nextNodeRef;
         headNode.nextNodeRef = currNode;


   // Get location pointed by nextNodeRef                                                             
   public ItemNode getNext() {
      return this.nextNodeRef;
   }
   
   public void printNodeData() {
      System.out.println(this.item);
   }
}

CodePudding user response：

The issue comes from the fact that you need to navigate to the final node of the list before appending the new node.

You can do this as such:

public void insertAtEnd(ItemNode headNode, ItemNode currNode) {
  while(headNode.nextNodeRef != null) headNode = headNode.nextNodeRef;
  headNode.nextNodeRef = currNode;
}

Hope this helps. If you need any clarifications feel free to ask.

CodePudding user response：

You should pass your lastNode as an argument instead of headNode so you can get an easy reference to the current last element

public void insertAtEnd(ItemNode lastNode, ItemNode currNode){
   lastNode.nextNodeRef = currNode;