CopyOnWriteList-JDK1.8

    private static class CopyOnWriteList<E>
    {
        private transient ReentrantLock lock = new ReentrantLock();

        private transient volatile Object array[];

        CopyOnWriteList()
        {
            array = new Object[0];
        }

        Object[] getArray()
        {
            return array;
        }

        void setArray(Object[] objs)
        {
            array = objs;
        }

        int sizeof()
        {
            return getArray().length;
        }

        boolean empty()
        {
            return sizeof() == 0;
        }

        @SuppressWarnings("unchecked")
        E get(int index)
        {
            return (E) getArray()[index];
        }

        boolean set(E e, int index)
        {
            final ReentrantLock lock = this.lock;
            try
            {
                lock.lock();
                Object[] elements = getArray();
                E oldValue = (E) elements[index];
                if (oldValue != e)
                {
                    int length = elements.length;
                    Object[] newElements = Arrays.copyOf(elements, length);
                    newElements[index] = e;
                    setArray(newElements);
                }
                else
                {
                    // 内存的可见性通过volatile的语义来实现,而不是数组的内容
                    setArray(elements);
                }

                return true;
            }
            finally
            {
                lock.unlock();
            }
        }

        boolean add(E e)
        {
            final ReentrantLock lock = this.lock;
            try
            {
                lock.lock();
                Object[] elements = getArray();
                int length = elements.length;
                // Math.min(original.length, newLength)
                Object[] newElements = Arrays.copyOf(elements, length + 1);
                newElements[length] = e;
                setArray(newElements);
                return true;
            }
            finally
            {
                lock.unlock();
            }

        }

    }