public class ExtLinkedList<E> {

	// 連結串列實際儲存元素
	private int size;
	// 第一個元素(頭節點，為了查詢)
	private Node first;
	// 最後一個元素（尾節點,為了新增）
	private Node last;

	// add
	public void add(E e) {
		Node node = new Node();//
		node.object = e;
		if (first == null) {
			// 新增第一個元素
			// 給第一個元素賦值給node節點
			first = node;

			// 以一個元素的首尾都是其本身
		} else {
			// 新增第二個或以上資料
			node.prev = last;
			last.next = node;// 上一個元素的next賦值
		}
		last = node;
		size++;
	}

	// 下標新增
	public void add(int index, E e) {
		// 下標的驗證
		checkElementIndex(index);
		/*if (index == size) {//
			add(e);
		}*/
		Node oldNode = getNode(index);// 原本下標index的節點 node2
		if (oldNode != null) {
			//Node oldNextNode = oldNode.next;// nodel3
			Node oldPrevNode = oldNode.prev;// node1
			Node newNode = new Node();// node4
			newNode.object = e;
			// node4的下一個節點
			newNode.next = oldNode;
			if (oldPrevNode == null) {
				first = newNode;
			} else {
				// node4的上一個節點
				newNode.prev = oldPrevNode;
				// node1的下個節點
				oldPrevNode.next = newNode;
			}

			// node2的下個節點
			oldNode.prev = newNode;
		}
		size++;
	}

	// get
	public Object get(int index) throws Exception {
		if (!isElementIndex(index))
			throw new IndexOutOfBoundsException("越界了");
		Node node = null;
		if (first != null) {
			node = first;
			for (int i = 0; i < index; i++) {
				node = node.next;
			}
		}

		return node.object;
	}

	public void remove(int index) throws Exception {
		if (!isElementIndex(index))
			throw new IndexOutOfBoundsException("越界了");
		ExtLinkedList.Node oldNode = getNode(index);
		if (oldNode != null) {
			// 獲取刪除節點的上下節點
			// node3
			ExtLinkedList.Node nextNode = oldNode.next;
			// node1
			ExtLinkedList.Node prevNode = oldNode.prev;
			if (prevNode != null) {
				prevNode.next = nextNode;
				oldNode.prev = null;
			} else {
				first = nextNode;
			}
			if (nextNode != null) {
				nextNode.prev = prevNode;
				oldNode.next = null;
			} else {
				last = prevNode;
			}
			nextNode.object = null;
			size--;
		}
		/*
		 * oldNode.prev.next = oldNode.next; oldNode.next.prev = oldNode.prev;
		 */
	}

	// 獲取node
	public Node getNode(int index) {
		if (!isElementIndex(index))
			throw new IndexOutOfBoundsException("越界了");
		Node node = null;
		if (first != null) {
			node = first;
			for (int i = 0; i < index; i++) {
				node = node.next;
			}
		}
		return node;
	}

	public int getSize() {
		return size;
	}

	// 連結串列節點儲存元素
	private static class Node {
		Object object;// 當前元素
		Node prev;// 上一個元素
		Node next;// 寫一個元素
	}

	private void checkElementIndex(int index) {
		if (!isElementIndex(index))
			throw new IndexOutOfBoundsException("越界");
	}

	private boolean isElementIndex(int index) {
		return index >= 0 && index < size;
	}

	private String outOfBoundsMsg(int index) {
		return "Index: " + index + ", Size: " + size;
	}

	public static void main(String[] args) throws Exception {
		ExtLinkedList extLinkedList = new ExtLinkedList();
		extLinkedList.add("a");
		extLinkedList.add("b");
		extLinkedList.add("c");
		extLinkedList.add("e");
	
		System.out.println("前"+extLinkedList.size);
		System.out.println(extLinkedList.get(3));
		extLinkedList.add(3, "d");
		System.out.println("後"+extLinkedList.size);
		System.out.println(extLinkedList.get(3));
		/*for (int i = 0; i < extLinkedList.size-1; i++) {
			Object object = extLinkedList.get(i);
			System.out.println(object);
		}*/
		/*
		 * for (int i = 0; i < extLinkedList.size; i++) {
		 * System.out.println("--" + extLinkedList.get(i)); }
		 */

	}
}