A very basic implementation of a doubly linked list.

DoublyLinkedList.java

package code;

public class DoublyLinkedList<E> {

    private static class Node<E> {
        E value;
        Node<E> next;
        Node<E> previous;
    }

    private Node<E> head;
    private Node<E> last;

    public DoublyLinkedList() {
        head = null;
        last = null;
    }

    public void prepend(E value) {
        Node<E> newNode = new Node<>();
        newNode.value = value;
        if (head == null) {
            head = last = newNode;
        } else {
            newNode.next = head;
            this.head.previous = newNode;
            this.head = newNode;
        }
    }

    public void append(E value) {
        var newNode = new Node<E>();
        newNode.value = value;
        if (head == null) {
            head = last = newNode;
        } else {
            newNode.previous = this.last;
            this.last.next = newNode;
            this.last = newNode;
        }
    }

    public boolean isEmpty() {
        return head == null;
    }

    public String toString() {
        var r = "";
        Node<E> current = last;
        while (current != null) {
            r += current.value;
            current = current.previous;
        }
        return r;
    }

    public static void main(String[] args) {
        DoublyLinkedList<String> ls = new DoublyLinkedList<>();
        ls.append("Dies ");
        ls.append("ist ");
        ls.append("ein ");
        ls.append("Test ");
        ls.prepend("Text: ");

        /*
        // after implementing "remove(int index)":
        System.out.println(ls); // Test ein ist Dies Text:
        ls.remove(0);
        System.out.println(ls); // Test ein ist Dies
        ls.remove(1);
        System.out.println(ls); // Test ein Dies
        ls.remove(2);
        System.out.println(ls); // ein Dies
        ls.remove(0);
        System.out.println(ls); // ein
        ls.remove(0);
        System.out.println(ls); // 
        */
    }
}