如何序列化类型X的列表，填充Y类型的对象，它扩展X，并在反序列化时仍然获得Y元素？

Question

I have this list

LinkedList<ASD> list = new LinkedList<ASD>();

then, I add some objects which extend ASD

BSD bsd = new BSD(); // BSD extends ASD
list.add(bsd);

and serialize list.

How can I get it to serialize and deserialize teh bsd element as BSD and not as ASD?

Answer 1

It is not a problem. All objects that you want to serialize must be instances of classes that implement Serializable . LinkedList does it. Declare either ASD or BSD (it does not matter in your case) to implement Serializable and try. Everything should work.

Answer 2

As noted by AlexR, everything is fine:

class ASD implements Serializable {
  private static final long serialVersionUID = 1L;
}

class BSD extends ASD {
  private static final long serialVersionUID = 1L;
}

LinkedList<ASD> list = new LinkedList<ASD>();
list.add(new BSD())

Now, if you serialize list , and later deserialize it, its elements will be of the correct type BSD .

Furthermore, the generic type argument (the <ASD> thing) is not saved during the serialization. The serialization procedure will only remember that list is a LinkedList object. What this means is that you can serialize an object of type LinkedList<ASD> and then deserialize it as LinkedList<BSD> (or even as eg LinkedList<Integer> ). An exception can be thrown later, though, if you try to access an element of the list that cannot be cast to the newly specified generic type.

Finally, I'm just saying this is doable, not that it is a good practice :)