模仿LinkList实现一个双向链表

实现一个双向链表

直接看代码，可以根据注释整理思路

package cn.com.suanfa;

/**
 * 实现一个简单的链表
 */
public class LinkListYsx<E> {

    private NodeYsx<E> first;
    private NodeYsx<E> last;
    int size = 0;

    /**
     * 获取指定下标的值
     * @param index
     * @return
     */
    public E get(int index){
        if (checkIndex(index)){
            NodeYsx<E> nodeYsx = node(index);
            return nodeYsx.obj;
        }else {
            return null;
        }
    }

    /**
     * 在链表头部新增节点
     * @param obj
     */
    public void addFirst(E obj){
        NodeYsx<E> f = first;
        NodeYsx<E> newNodeYsx = new NodeYsx<E>(null, obj, f);
        first = newNodeYsx;
        if (f == null){
            last = newNodeYsx;
        }else {
            f.prev = newNodeYsx;
        }
        size++;
    }

    /**
     * 在链表尾部新增节点
     * @param obj
     */
    public void addLast(E obj){
        NodeYsx<E> l = last;
        NodeYsx<E> newNodeYsx = new NodeYsx<>(l, obj, null);
        last = newNodeYsx;
        if (l == null){
            first = newNodeYsx;
        }else {
            l.next = newNodeYsx;
        }
        size++;
    }

    /**
     * 在链表指定节点新增节点
     * @param index
     * @param obj
     */
    public void add(int index, E obj) {
        if (checkIndex(index)){
            NodeYsx<E> nodeYsx = node(index);
            NodeYsx<E> prev = nodeYsx.prev;
            NodeYsx<E> newNodeYsx = new NodeYsx<>(prev, obj, nodeYsx);
            prev.next = newNodeYsx;
            nodeYsx.prev = newNodeYsx;
            size++;
        }
    }

    /**
     * 删除链表头节点
     * @return
     */
    public E removeFirst(){
        NodeYsx<E> f = first;
        E value = f.obj;
        NodeYsx<E> next = f.next;
        f.obj = null;
        f.next = null;
        if (next == null){
            last = null;
        }else {
            next.prev = null;
        }
        size--;
        return value;
    }

    /**
     * 删除链表尾节点
     * @return
     */
    public E removeLast(){
        NodeYsx<E> l = last;
        E value = l.obj;
        NodeYsx<E> prev = l.prev;
        l.obj = null;
        l.prev = null;
        last = prev;
        if (prev == null){
            first = null;
        }else {
            prev.next = null;
        }
        size--;
        return value;
    }

    /**
     * 判断下标是否超出链表范围
     * @param i
     * @return
     * @throws Exception
     */
    private boolean checkIndex(int i) {
        if (i >= 0 && i < size){
            return true;
        }else {
            throw new IndexOutOfBoundsException();
        }
    }

    /**
     * 获取指定下标的节点
     * @param index
     * @return
     */
    private NodeYsx<E> node(int index){
        if (index < size / 2){
            NodeYsx<E> result = first;
            for (int i = 0; i < index; i++) {
                result = result.next;
            }
            return result;
        }else{
            NodeYsx<E> result = last;
            for (int i = size-1; i > index; i--) {
                result = result.prev;
            }
            return result;
        }
    }

    /**
     * 链表的Node节点
     * @param 
     */
    private class NodeYsx<E> {
        private NodeYsx<E> prev;
        private E obj;
        private NodeYsx<E> next;

        public NodeYsx(NodeYsx<E> prev, E obj, NodeYsx<E> next) {
            this.prev = prev;
            this.obj = obj;
            this.next = next;
        }
    }
}