基本数据结构——链表

　　链表中各个对象按线性顺序排列，链表的顺序是由各个对象里的指针决定的。

链表中每个元素都是一个对象。每个对象中包含一个关键字key和两个指针prev, next分别指针这个对象的前一个对象和下一个对象。关键方法的实现代码如下：

//定义插入，删除，查找方法
public class List<E> {

    private Node<E> first;    //Pointer to first node.
    private Node<E> last;    //Pointer to last node.
    private int size;
    
    public void insertFirst(E e) {
        Node<E> f = first; 
        Node<E> newNode = new Node<E>(null, f, e);
        first = newNode;
        if(f == null){
            last = newNode;
        }else{
            f.prev = newNode;
        }
        
        size++;
    }
    
    public Node<E> research(E e) {
        Node<E> temp = first;
        while(temp != null && temp.key != e ) {
            temp = temp.next;
        }
        return temp;
    }
    
    public void deleteLast() {
        Node<E> l = last;
        final E element = l.key;
        final Node<E> prev = l.prev;
        l.key = null;
        l.prev = null; // help GC
        last = prev;
        if (prev == null)
            first = null;
        else
            prev.next = null;
        size--;

    }
    
    private static class Node<E> {
        Node<E> prev;
        Node<E> next;
        E key;
        
        public Node(Node<E> prev, Node<E> next, E key) {
            this.prev = prev;
            this.next = next;
            this.key = key;
        }        
    }
    
/*    public static void main(String[] args) {
        List<Integer> list = new List<>();
        list.insertFirst(1);
        list.insertFirst(2);
        list.insertFirst(3);
        list.insertFirst(4);
        list.insertFirst(5);
        
        Node<Integer> node = list.research(1);
        System.out.println(node);
        System.out.println(list.size);
        list.deleteLast();
        node = list.research(1);
        System.out.println(node);
        System.out.println(list.size);
    }*/

    
}