java - LinkedList (built from scratch) add() not working

Question

I'm working on a class assignment where I must build a singly linkedlist class from scratch. My problem here is that my add() method isn't quite working when I iterate through a series of items and add them to a linkedlist. More specifically, 1) it is duplicating the first one in a series, and 2) it is not adding the last one in a series. What is wrong with my add() method in the ManualLinkedList class?

public class test {
    static class ManualLinkedList<T> {
        private static class Node<T> {
            T item;
            Node<T> next;
            Node<T> prev;

            public T getItem() {
                    return item;
                }
            public ManualLinkedList.Node<T> getNext() {
                    return next;
                }

            Node(Node<T> prev, T element, Node<T> next) {
                this.item = element;
                this.next = next;
                this.prev = prev;
            }
        }

        Node<T> head;
        Node<T> tail;
        int size = 0;

        public void add(T t) {
            final Node<T> l = tail;
            final Node<T> newNode = new Node<>(l, t, null);
            tail = newNode;
            if (l == null) {
                head = newNode;
            }
            else {
                l.next = newNode;
            }
            size++;
        }

        public int size() { return size; }

        public T getContentFromPosition(int position) {
            Node<T> np = head;
            T result = head.getItem();

            if (position == size) {
                result = tail.getItem();
            }
            for (int i = 1; i < size; i++) {
                if (i == position) {
                    result = np.getItem();
                }
                np = np.getNext();
            }
            return result;
        }
    } //end ManualLinkedList class


    public static void main(String[] args) {
        ManualLinkedList<Integer> test = new ManualLinkedList<>();
        test.add(1);
        test.add(2);
        test.add(3);
        test.add(4);
        test.add(5);
        test.add(6);
        test.add(7);
        test.add(8);

        for (int i =0; i < test.size; i++){
            System.out.println(test.getContentFromPosition(i));
        }
    }
}

Expected Output:

1
2
3
4
5
6
7
8

Actual Output:

1
1  // notice the duplicate first item
2
3
4
5
6
7  // notice the missing 8, or the last input

question from:https://stackoverflow.com/questions/66057565/linkedlist-built-from-scratch-add-not-working

Answer 1

Primary Issues

1. index is used as 0..size-1 during invocation
2. for loop in getContentFromPosition should be from 0..size-1
3. The usage of size == position is irrelevant in getContentFromPosition

Code

        public T getContentFromPosition(int position) {
            if (position >= size) {
                return null;
            }
            Node<T> np = head;
            T result = head.getItem();
            if (position == size - 1) {
                result = tail.getItem();
            }
            for (int i = 0; i < size; i++) {
                if (i == position) {
                    result = np.getItem();
                    break;
                }
                np = np.next;
            }
            return result;
        }
    } //end ManualLinkedList class


    public static void main(String[] args) {
        ManualLinkedList<Integer> test = new ManualLinkedList<>();
        test.add(1);
        test.add(2);
        test.add(3);
        test.add(4);
        test.add(5);
        test.add(6);
        test.add(7);
        test.add(8);

        for (int i = 0; i < test.size; i++){
            System.out.println(test.getContentFromPosition(i));
        }
    }