public boolean add(E e) {
       //擴(kuò)容
        ensureCapacityInternal(size + 1);  // Increments modCount!!
        elementData[size++] = e;
        return true;
    }

    private void ensureCapacityInternal(int minCapacity) {
        ensureExplicitCapacity(calculateCapacity(elementData, minCapacity));
    }

   private static int calculateCapacity(Object[] elementData, int minCapacity) {
        //如果傳入的是個(gè)空數(shù)組則最小容量取默認(rèn)容量與minCapacity之間的最大值
        if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
            return Math.max(DEFAULT_CAPACITY, minCapacity);
        }
        return minCapacity;
    }

 private void ensureExplicitCapacity(int minCapacity) {
          modCount++;
          // 如果最小需要空間比elementData的內(nèi)存空間要大，則需要擴(kuò)容
          if (minCapacity - elementData.length > 0)
              //擴(kuò)容
              grow(minCapacity);
      }

 private void grow(int minCapacity) {
          // 獲取到ArrayList中elementData數(shù)組的內(nèi)存空間長(zhǎng)度
          int oldCapacity = elementData.length;
         // 擴(kuò)容至原來(lái)的1.5倍
         int newCapacity = oldCapacity + (oldCapacity >> 1);
         // 再判斷一下新數(shù)組的容量夠不夠，夠了就直接使用這個(gè)長(zhǎng)度創(chuàng)建新數(shù)組，
          // 不夠就將數(shù)組長(zhǎng)度設(shè)置為需要的長(zhǎng)度
         if (newCapacity - minCapacity < 0)
             newCapacity = minCapacity;
         //若預(yù)設(shè)值大于默認(rèn)的最大值檢查是否溢出
         if (newCapacity - MAX_ARRAY_SIZE > 0)
             newCapacity = hugeCapacity(minCapacity);
         // 調(diào)用Arrays.copyOf方法將elementData數(shù)組指向新的內(nèi)存空間時(shí)newCapacity的連續(xù)空間
         // 并將elementData的數(shù)據(jù)復(fù)制到新的內(nèi)存空間
         elementData = Arrays.copyOf(elementData, newCapacity);
     }
復(fù)制代碼

//節(jié)點(diǎn)
public class Node {
	Node previous;//前繼，指向前一個(gè)Node
	Object data;//節(jié)點(diǎn)數(shù)據(jù)
	Node next;//后繼，指向后一個(gè)Node
	public Node() {
	}
	public Node(Node previous, Object data, Node next) {
		super();
		this.previous = previous;
		this.data = data;
		this.next = next;
	} 
}

public class MyLinkedList {
	private Node first;//首節(jié)點(diǎn)
	private Node last;//尾節(jié)點(diǎn)
	private int size;//鏈表大小
	public MyLinkedList() {
		first = null;
		last = null;
		size = 0;
	}
}

public void add(Object obj){
		Node node = new Node(null,null,null);
		if(first==null){//first=null,說(shuō)明LinkedList中沒(méi)有一個(gè)節(jié)點(diǎn)
			node.data = obj;
			first = node;
			last = node;//第一個(gè)節(jié)點(diǎn)和最后一個(gè)節(jié)點(diǎn)都是node
			size++;
		}else{
			node.data = obj;
			last.next = node;//和最后一個(gè)連接起來(lái)
			node.previous = last;
			last = node;//當(dāng)前節(jié)點(diǎn)變?yōu)槟┪补?jié)點(diǎn)
			size++;
		}

public Node get(int index) {
		RangeCheck(index);
		Node temp = null;
		if(index < (size>>1)){//改進(jìn)的遍歷方法，右移運(yùn)算符的巧用
			temp = first;
			for(int i=0;i<index;i++){
				temp = temp.next;
			}
		}else {
			temp = last;
			for(int i=size-1;i>index;i--){
				temp = temp.previous;
			}
		}
		return temp;
	}

public void add(int index,Object obj) {
		RangeCheck(index);//對(duì)傳入的索引必須進(jìn)行檢查，判斷是否越界
		Node node = new Node(null,null,null);
		node.data = obj;
		Node node2=first;
		for(int i=0;i<index-1;i++){
			node2 = node2.next;
		}
		node.next = node2.next;
		node2.next.previous=node;
		node2.next = node;
		node.previous=node2;
		size++;
	}

private void RangeCheck(int index) {
		if(index<0||index >= size){
			throw new IndexOutOfBoundsException("IndexOutOfBounds"+index);//不合法則拋出異常
		}
	}

public boolean remove(Object obj) {
		Node node = first;
		if(obj==null){
			while(node!=null){
				if(node.data==null){
					removefast(node);
					return true;
				}
				node = node.next;
			}
		}else {
			while(node!=null){
				if(obj.equals(node.data)){
					removefast(node);
					return true;
				}
				node = node.next;
			}
		}
		return false;
	}
	private void removefast(Node node){
		node.previous.next=node.next;
		size--;
		node.data=null;
		node.previous = node.next = null;
	}

public Object set(int index,Object obj) {
		Node node = get(index);
		Object oldObject=node.data;
		node.data = obj;
		return oldObject;
	}