public class Program { public static void main(String[] args) { DoublyLinkedList dlk = new DoublyLinkedList<>(); // add a node dlk.addFirst(10); System.out.println(dlk.first()); System.out.println(dlk.size()); // add some nodes dlk.addLast(20); dlk.addLast(30); // traversing dlk.printAllElement(); } } class DoublyLinkedList{ // nested class private static class Node{ private E element; private Node next; private Node prev; public Node(E e, Node p, Node n){ element = e; next = n; prev = p; } public E getElement(){return element;} public Node getNext(){return next;} public Node getPrev(){return prev;} public void setNext(Node n){next = n;} public void setPrev(Node n){prev = n;} } private Node header; private Node trailer; private int size = 0; public DoublyLinkedList(){ header = new Node<>(null, null, null); trailer = new Node<>(null, header, null); header.setNext(trailer); } public int size(){return size;} public boolean isEmpty(){return size == 0;} public E first(){ if (isEmpty()) return null; return header.getNext().getElement(); } public E last(){ if (isEmpty()) return null; return trailer.getPrev().getElement(); } public void addFirst(E e){ addBetween(e, header, header.getNext()); } public void addLast(E e){ addBetween(e, trailer.getPrev(), trailer); } public E removeFirst(){ return remove(header.getNext()); } public E removeLast(){ return remove(trailer.getPrev()); } public void printAllElement(){ if(isEmpty()){ System.out.println("No elements now."); return ; } // traversing Node temp = header.getNext(); int count = 0; while(temp.getElement() != null){ count++; System.out.print(count + ": " + temp.getElement() + "\t"); temp = temp.getNext(); } System.out.println(); } private void addBetween(E e, Node predecessor, Node successor){ Node n = new Node<>(e, predecessor, successor); predecessor.setNext(n); successor.setPrev(n); size++; } private E remove(Node node){ if(isEmpty()) return null; else{ Node prev = node.getPrev(); Node next = node.getNext(); prev.setNext(next); next.setPrev(prev); size--; return node.getElement(); } } }