为什么CopyOnWriteArrayList需要自定义序列化

Question

我已经阅读了CopyOnWriteArrayList（JDK 1.8）的源代码，我发现它实现了writeObject和readObject。我的问题是为什么CopyOnWriteArrayList需要自定义序列化？

   /**
 * Saves this list to a stream (that is, serializes it).
 *
 * @param s the stream
 * @throws java.io.IOException if an I/O error occurs
 * @serialData The length of the array backing the list is emitted
 *               (int), followed by all of its elements (each an Object)
 *               in the proper order.
 */
private void writeObject(java.io.ObjectOutputStream s)
    throws java.io.IOException {

    s.defaultWriteObject();

    Object[] elements = getArray();
    // Write out array length
    s.writeInt(elements.length);

    // Write out all elements in the proper order.
    for (Object element : elements)
        s.writeObject(element);
}

/**
 * Reconstitutes this list from a stream (that is, deserializes it).
 * @param s the stream
 * @throws ClassNotFoundException if the class of a serialized object
 *         could not be found
 * @throws java.io.IOException if an I/O error occurs
 */
private void readObject(java.io.ObjectInputStream s)
    throws java.io.IOException, ClassNotFoundException {

    s.defaultReadObject();

    // bind to new lock
    resetLock();

    // Read in array length and allocate array
    int len = s.readInt();
    Object[] elements = new Object[len];

    // Read in all elements in the proper order.
    for (int i = 0; i < len; i++)
        elements[i] = s.readObject();
    setArray(elements);
}

感谢。

Answer 1

我得到了答案。如果我们使用默认序列化，则可以序列化许多null元素。