实现简答LinkedList

package com.表栈和队列;


import java.util.Iterator;
/**
 * 实现LinkedList
 * 60页
 * @author zj
 *
 * @param <T>
 */
public class MyLinkedList<T> implements Iterable<T>{

private int theSize; //集合大小

private int modCount = 0;//代表自从构造以来对链表所做的改变次数

private Node<T> beginMarker;//头节点

private Node<T> endMarker;//尾节点

/**
* 
* 连接到前一个node和下一个Node
* @author Administrator
*
* @param <T>
*/
private static class Node<T>{
public T data;
public Node<T> prev;//上一个链
public Node<T> next;//下一个链

public Node(T d ,Node<T> p,Node<T> n){
data = d ;
prev = p ;
next = n;
}

}

public MyLinkedList(){
clear();
}

private void clear() {
// TODO Auto-generated method stub
beginMarker = new Node<T>(null, null, null);
endMarker = new Node<T>(null, beginMarker, null);
beginMarker.next = endMarker;

theSize = 0;
modCount++;
}

private int size(){
return theSize;
}


public boolean isEmpty(){
return size() == 0;
}

public boolean add(T t){
add(size(),t);
return true;
}
private void add(int idx, T t) {
// TODO Auto-generated method stub
addBefore( getNode( idx ), t );
}

private T get(int idx){
return getNode(idx).data;
}

private T set(int idx,T newVal){
Node<T> p = getNode(idx);
T  oldVal = p.data;
p.data = newVal;
return oldVal;
}
public T remove(int idx){
return remove(getNode(idx));
}
private T remove(Node<T> p) {
// TODO Auto-generated method stub
p.next.prev = p.prev;
p.prev.next = p.next;
theSize--;
modCount++;
return p.data;

}


/**
* 从下标0開始计算
* 通过获取一个新节点，然后改变指针完毕一个双链表的插入操作
* @param p
* @param t
*/
private void addBefore(Node<T> p, T t) {
// TODO Auto-generated method stub
Node<T> newNode = new Node<T>(t,p.prev,p);
newNode.prev.next = newNode;//新节点的上一个节点中指向下一节点的位置
p.prev = newNode;//插入位置节点指向上一节点的位置
theSize++;
modCount++;
}


/*
* 依据索引获取节点
* 假设索引在表的前半部分。那么将向后的方向遍历链表
* 否则将向末尾往回遍历
*/
private Node<T> getNode(int idx) {
// TODO Auto-generated method stub
Node<T> p;

if(idx < 0 || idx > size()){
throw new  IndexOutOfBoundsException();
}

if(idx < size()/2){
p = beginMarker.next;
for(int i=0;i<idx;i++){
p = p.next;
}
}else{
p = endMarker;
for(int i=size();i>idx;i--){
p = p.prev;
}
}
return p;
}


@Override
public Iterator<T> iterator() {
// TODO Auto-generated method stub
return new LinkedListIterator();
}
private class LinkedListIterator implements java.util.Iterator<T>{
private Node<T> current = beginMarker.next; //当前节点
private int expectedModCount = modCount;
private boolean okToRemove = false;

@Override
public boolean hasNext() {
// TODO Auto-generated method stub
return current!= endMarker;//当前节点是否等于最后节点
}


@Override
public T next() {
// TODO Auto-generated method stub
if(modCount != expectedModCount)
throw new java.util.ConcurrentModificationException();
if(!hasNext())
throw new java.util.NoSuchElementException();

T nextItem = current.data;
current = current.next;
okToRemove = true;
return nextItem;

}


@Override
public void remove() {
// TODO Auto-generated method stub
if(modCount != expectedModCount)
throw new java.util.ConcurrentModificationException();
if(!okToRemove)
throw new IllegalStateException();
MyLinkedList.this.remove(current.prev);
okToRemove = false;
expectedModCount++;
}

}
public static void main(String[] args) {
MyLinkedList<Integer> ml = new MyLinkedList<Integer>();
ml.add(1);
ml.add(2);
ml.add(3);
ml.add(1, 10);
for(Integer i :ml){
System.out.println(i);
}
}
}