一。LinkedList：
数据结构是双向链表

transient Node<E> first;

    /**
     * Pointer to last node.
     * Invariant: (first == null && last == null) ||
     *            (last.next == null && last.item != null)
     */
    transient Node<E> last;

list的增删改查
1.增（加元素）

/**
     * Inserts the specified element at the beginning of this list.
     *
     * @param e the element to add
     */
    public void addFirst(E e) {
        linkFirst(e);
    }

    /**
     * Appends the specified element to the end of this list.
     *
     * <p>This method is equivalent to {@link #add}.
     *
     * @param e the element to add
     */
    public void addLast(E e) {
        linkLast(e);
    }
/**
     * Links e as first element.
     */
    private void linkFirst(E e) {
        final Node<E> f = first;
        final Node<E> newNode = new Node<>(null, e, f);
        first = newNode;
        if (f == null)
            last = newNode;
        else
            f.prev = newNode;
        size++;
        modCount++;
    }
/**
     * Links e as last element.
     */
    void linkLast(E e) {
        final Node<E> l = last;
        final Node<E> newNode = new Node<>(l, e, null);
        last = newNode;
        if (l == null)
            first = newNode;
        else
            l.next = newNode;
        size++;
        modCount++;
    }

其他的方法暂时不罗列
2.删除元素

public E remove(int index) {
        checkElementIndex(index);
        return unlink(node(index));
    }

3.修改某个元素值

/**
     * Replaces the element at the specified position in this list with the
     * specified element.
     *
     * @param index index of the element to replace
     * @param element element to be stored at the specified position
     * @return the element previously at the specified position
     * @throws IndexOutOfBoundsException {@inheritDoc}
     */
    public E set(int index, E element) {
        checkElementIndex(index);
        Node<E> x = node(index);
        E oldVal = x.item;
        x.item = element;
        return oldVal;
    }

4.查询

public E get(int index) {
        checkElementIndex(index);
        return node(index).item;
    }

二。ArrayList
数据结构是 transient Object[] elementData;数组
默认数组的容量大小是10；

/**
     * Default initial capacity.
     */
    private static final int DEFAULT_CAPACITY = 10;

如果容量不够，会扩容

 int newCapacity = oldCapacity + (oldCapacity >> 1);

<< : 左移运算符，num << 1,相当于num乘以2

 :     右移运算符，num >> 1,相当于num除以2

: 无符号右移，忽略符号位，空位都以0补齐
每次扩容相当于是原来的3/2倍；
ArrayList的增删改查
1,增

/**
     * Inserts the specified element at the specified position in this
     * list. Shifts the element currently at that position (if any) and
     * any subsequent elements to the right (adds one to their indices).
     *
     * @param index index at which the specified element is to be inserted
     * @param element element to be inserted
     * @throws IndexOutOfBoundsException {@inheritDoc}
     */
    public void add(int index, E element) {
        if (index > size || index < 0)
            throw new IndexOutOfBoundsException(outOfBoundsMsg(index));

        ensureCapacityInternal(size + 1);  // Increments modCount!!
        System.arraycopy(elementData, index, elementData, index + 1,
                         size - index);
        elementData[index] = element;
        size++;
    }

2.删

public E remove(int index) {
        if (index >= size)
            throw new IndexOutOfBoundsException(outOfBoundsMsg(index));

        modCount++;
        E oldValue = (E) elementData[index];

        int numMoved = size - index - 1;
        if (numMoved > 0)
            System.arraycopy(elementData, index+1, elementData, index,
                             numMoved);
        elementData[--size] = null; // clear to let GC do its work

        return oldValue;
    }

3.改

public E set(int index, E element) {
        if (index >= size)
            throw new IndexOutOfBoundsException(outOfBoundsMsg(index));

        E oldValue = (E) elementData[index];
        elementData[index] = element;
        return oldValue;
    }

4.查询

public E get(int index) {
        if (index >= size)
            throw new IndexOutOfBoundsException(outOfBoundsMsg(index));

        return (E) elementData[index];
    }