public boolean add(E e) {

        ensureCapacityInternal(size + );            //ensureCapacityInternal用来调整容量

        elementData[size++] = e;

        return true;

    }

private void ensureCapacityInternal(int minCapacity) {

        if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {

            minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);

        }

        ensureExplicitCapacity(minCapacity);

    }

    private void ensureExplicitCapacity(int minCapacity) {

        modCount++;

        // overflow-conscious code

        if (minCapacity - elementData.length > )

            grow(minCapacity);

    }

private void grow(int minCapacity) {                         //增加容量

        // overflow-conscious code

        int oldCapacity = elementData.length;

        int newCapacity = oldCapacity + (oldCapacity >> );

        if (newCapacity - minCapacity < )

            newCapacity = minCapacity;                       //如果容量够了，就直接以这个长度创建数组

        if (newCapacity - MAX_ARRAY_SIZE > )                //如果容量不够，再进行扩充

            newCapacity = hugeCapacity(minCapacity);

        // minCapacity is usually close to size, so this is a win:

        elementData = Arrays.copyOf(elementData, newCapacity);//最后将原来的复制到新的数组中

    }

private static int hugeCapacity(int minCapacity) {

        if (minCapacity < ) // overflow

            throw new OutOfMemoryError();

        return (minCapacity > MAX_ARRAY_SIZE) ?

            Integer.MAX_VALUE :

            MAX_ARRAY_SIZE;

    }