LinkedList

LinkedList双向链表的实现

 每个节点有由三个组成

private static final class Link<ET> {
        ET data;

        Link<ET> previous, next;

        Link(ET o, Link<ET> p, Link<ET> n) {
            data = o;
            previous = p;
            next = n;
        }
    }

  public boolean add(E object) {
         Link<E> oldLast = voidLink.previous;//获得最后一个节点
        Link<E> newLink = new Link<E>(object, oldLast, voidLink);// 生成一个新的节点
        voidLink.previous = newLink;
        oldLast.next = newLink;
        size++;
        modCount++;
        return true;
    }

  public void addFirst(E object) {
        Link<E> oldFirst = voidLink.next;//获得第一个节点
        Link<E> newLink = new Link<E>(object, voidLink, oldFirst);
        voidLink.next = newLink;
        oldFirst.previous = newLink;
        size++;
        modCount++;
    }

  public void add(int location, E object) {
        if (0 <= location && location <= size) {
            Link<E> link = voidLink;
            if (location < (size / 2)) {
                for (int i = 0; i <= location; i++) {
                    link = link.next;
                }
            } else {
                for (int i = size; i > location; i--) {
                    link = link.previous;
                }
            }
            Link<E> previous = link.previous;
            Link<E> newLink = new Link<E>(object, previous, link);
            previous.next = newLink;
            link.previous = newLink;
            size++;
            modCount++;
        } else {
            throw new IndexOutOfBoundsException();
        }
    }

 /**
     * Constructs a new empty instance of {@code LinkedList}.
     */
    public LinkedList() {
        voidLink = new Link<E>(null, null, null);
        voidLink.previous = voidLink;
        voidLink.next = voidLink;
    }