I am working on a project for my Data Structures class that asks me to write a class to implement a linked list of ints.

• Use an inner class for the Node.
• Include the methods below.
• Write a tester to enable you to test all of the methods with whatever data you want in any order.

I have to create a method called "public void addToBack(int item)". This method is meant to "Add an Item to the end of the list" I have my code for this method down below. When I execute this method my list becomes empty. Does someone know what I did wrong and how to fix it?

import java.util.Random;
import java.util.Scanner;

public class LinkedListOfInts {
    Node head;
    Node tail;

    private class Node {
        int value;
        Node nextNode;

        public Node(int value, Node nextNode) {
            this.value = value;
            this.nextNode = nextNode;
        }

    }

    public LinkedListOfInts(LinkedListOfInts other) {
        Node tail = null;
        for (Node n = other.head; n != null; n = n.nextNode) {
            if (tail == null)
                this.head = tail = new Node(n.value, null);
            else {
                tail.nextNode = new Node(n.value, null);
                tail = tail.nextNode;
            }
        }
    }

    public LinkedListOfInts(int[] other) {
        Node[] nodes = new Node[other.length];
        for (int index = 0; index < other.length; index  ) {
            nodes[index] = new Node(other[index], null);
            if (index > 0) {
                nodes[index - 1].nextNode = nodes[index];
            }
        }

        head = nodes[0];
    }

    public LinkedListOfInts(int N, int low, int high) {
        Random random = new Random();
        for (int i = 0; i < N; i  )
            this.addToFront(random.nextInt(high - low)   low);
    }

    public void addToFront(int x) {
        head = new Node(x, head);
    }

    public void addToBack(int x) {
        if (head == null) {
            head = new Node(x, head);
            return;
        }
        tail = head;
        while (tail.nextNode != null) {
            tail = tail.nextNode;
        }
        tail.nextNode = new Node(x, tail);
    }

    public String toString() {
        String result = "";
        for (Node ptr = head; ptr != null; ptr = ptr.nextNode) {
            if (!result.isEmpty()) {
                result  = ", ";
            }
            result  = ptr.value;
        }
        return "["   result   "]";
    }

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        LinkedListOfInts list = new LinkedListOfInts(10, 1, 20);
        boolean done = false;
        while (!done) {
            System.out.println("1. Add to Back");
            System.out.println("2. toString");
            switch (input.nextInt()) {
            case 1:
                System.out.println("Add an Item to the Back of a List.");
                list.addToBack(input.nextInt());
                break;
            case 2:
                System.out.println("toString");
                System.out.println(list.toString());
                break;

            }
        }
    }
}

CodePudding user response：

When you add to the tail the nextNode should point to null

tail.nextNode = new Node(x, null);

At the moment you are having an endless loop