https://chikuwa-tech-study.blogspot.com/2021/05/java-linked-list.html

LinkedList.java

public class LinkedList<E> {
    private Node<E> first;
    private Node<E> last;
    private int size;

    public int size() {
        return this.size;
    }

    public E getFirst() {
        return this.first.getData();
    }

    public E getLast() {
        return this.last.getData();
    }

    private Node<E> getNode(int index) {
        if (index < 0 || index >= this.size) {
            throw new IndexOutOfBoundsException();
        }

        Node<E> currentNode = this.first;
        for (int i = 0; i < index; i++) {
            currentNode = currentNode.getNext();
        }
        return currentNode;
    }

    public E get(int index) {
        return getNode(index).getData();
    }

    public void add(E data) {
        Node<E> node = new Node<>(data);

        if (this.size == 0) {
            this.first = node;
        } else {
            this.last.setNext(node);
        }
        this.last = node;
        this.size++;
    }

    public void add(int index, E data) {
        if (index < 0 || index > this.size) {
            throw new IndexOutOfBoundsException();
        }

        if (index == this.size) {
            add(data);
            return;
        }

        Node<E> node = new Node<>(data);
        if (index == 0) {
            node.setNext(this.first);
            this.first = node;
        } else {
            Node<E> previousNode = getNode(index - 1);
            Node<E> nextNode = previousNode.getNext();
            previousNode.setNext(node);
            node.setNext(nextNode);
        }
        this.size++;
    }

    public void remove(int index) {
        if (index < 0 || index >= this.size) {
            throw new IndexOutOfBoundsException();
        }

        if (index == 0) {
            if (this.size == 1) {
                this.last = null;
            }
            this.first = this.first.getNext();
        } else {
            Node<E> previousNode = getNode(index - 1);
            Node<E> targetNode = previousNode.getNext();
            Node<E> nextNode = targetNode.getNext();
            previousNode.setNext(nextNode);

            if (index == size - 1) {
                this.last = previousNode;
            }
        }
        this.size--;
    }

    public void reverse() {
        Node<E> previousNode = null;
        Node<E> currentNode = this.first;
        Node<E> nextNode;

        while (currentNode != null) {
            nextNode = currentNode.getNext();
            currentNode.setNext(previousNode);
            previousNode = currentNode;
            currentNode = nextNode;
        }

        this.last = this.first;
        this.first = previousNode;
    }
    
    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        Node<E> node = this.first;
        while (node != null) {
            sb.append(node.toString()).append(" ");
            node = node.getNext();
        }
        
        return sb.toString();
    }
}

Node.java

public class Node<E> {
    private E data;
    private Node<E> next;

    public Node(E data) {
        this.data = data;
    }

    public E getData() {
        return data;
    }

    public Node<E> getNext() {
        return next;
    }

    public void setNext(Node<E> next) {
        this.next = next;
    }

    @Override
    public String toString() {
        return data.toString();
    }
}