base - 算法-双向链表（参考LinkedList）

世界上并没有完美的程序，但是我们并不因此而沮丧，因为写程序就是一个不断追求完美的过程。

public class TowList {
    private Node first;
    private Node last;
    private Integer size = 0;

    static class Node {
        private Node pre;
        private Node next;
        private String value;
        public Node (Node pre, String value, Node next) {
            this.pre = pre;
            this.value = value;
            this.next = next;
        }
    }

    public void addFirst (String value) {
        Node f = first;
        Node newNode = new Node(null, value, f);
        first = newNode;
        if (null == f) {
            last = newNode;
        } else {
            f.pre = newNode;
        }
        size++;
    }

    public void addLast (String value) {
        Node l = last;
        Node newNode = new Node(l, value, null);
        last = newNode;
        if (l == null) {
            first = newNode;
        } else {
            l.next = newNode;
        }
        size++;
    }

    public String removeFirst () {
        Node f = first;
        if (null == f) {
            throw new NoSuchElementException();
        }
        Node next = f.next;
        String value = f.value;
        f.next = null;
        f.value = null;
        first = next;
        if (null == next) {
            last = null;
        } else {
            next.pre = null;
        }
        size--;
        return value;
    }

    public String removeLast () {
        Node l = last;
        if (null == l) {
            throw new NoSuchElementException();
        }
        Node pre = l.pre;
        String value = l.value;
        l.pre = null;
        l.value = null;
        last = pre;
        if (null == pre) {
            first = null;
        } else {
            pre.next = null;
        }
        size--;
        return value;
    }

    public boolean hasNext () {
        if (size > 0) {
            return true;
        }
        return false;
    }

    public Integer size () {
        return size;
    }

    public static void main(String[] args) {
        TowList towList = new TowList();
        towList.addLast("3");
        towList.addLast("4");
        towList.addLast("5");

        System.out.println("size: " + towList.size());

//        while (towList.hasNext()) {
//            System.out.println(towList.removeFirst());
//        }

        while (towList.hasNext()) {
            System.out.println(towList.removeLast());
        }
    }