LinkedList自己实现（追加，插入，删除，遍历）

java1.8之前是双向循环链表，
java1.8之后是双向不循环链表

public class MyLinkedList {
	private Node head;
	private int size;
	private class Node {
		E data;
		Node next;	//后一个
		Node prev;	//前一个
		public Node(E e){
			data = e;
		}
	};



/**
 * 追加元素方法
 */
public boolean add( E e ){
	if( head == null ){
		//添加第一个元素
		head = new Node(e);
		//创建循环关系
		head.next = head;
		head.prev = head;
		size++;
		return true;
	}else{
		Node last = head.prev;
		Node node = new Node(e);
		head.prev = node;
		last.next = node;
		node.prev = last;
		node.next = head;
		size++;
		return true;
	}
}

/**
 * 插入元素
 */
public boolean add( int index, E e ){
	Node node = find(index);
	Node next = node;
	Node prev = node.prev;
	node = new Node(e);
	prev.next = node;
	node.next = next;
	next.prev = node;
	node.prev = prev;
	size++;
	return true;
}

/**
 * 删除元素
 */
public E remove(int index){
	if( index < 0 || index >= size ){
		throw new IndexOutOfBoundsException();
	}
	Node node = find(index);
	E e = node.data;
	node.prev.next = node.next;
	node.next.prev = node.prev;
	if( index == 0 ){	//删除头
		head = node.next;
	}
	//去掉引用
	node.next = null;
	node.prev = null;
	size--;
	return e;
}

/**
 * toString
 */
public String toString(){
	if( head == null ){
		return "[]";
	}
	StringBuilder stb = new StringBuilder("[");
	stb.append(head.data);
	Node node = head.next;
	for( int i = 1; i < size; i++ ){
		stb.append(",").append(node.data);
		node = node.next;
	}
	stb.append("]");
	return stb.toString();
}

/**
 *	公共方法
 * @param index
 * @return
 */
private Node find(int index) {
	Node node;
	//查找插入位置
	if( index>size>>1 ){	//反向查找
		node = head.prev;
		for( int i = size-1; i > index; i-- ){
			node = node.prev;
		}
	}else{		//正向查找
		node = head;
		for( int i = 0; i < index; i++ ){
			node = node.next;
		}
	}
	return node;
}
	
}