Java：哪些类必须实现Serializable

Question

I am currently trying to learn and understand how to store data from user input as a file.

Currently, I have the classes "movies" and "series" and the class "MediaLibrary".

Now's the question: Which classes have to implement Serializable?

Do I only have to implement it at MediaLibrary (since I store objects from the other classes in ArrayList's) or do the other classes need Serializable too?

Thanks for your help.

LevKaz

EDIT 1: What makes my question unique from the possible duplicate? In the possible duplicate the guy asked, why not all objects are serializable , since he doesn't wanted to write it in every single class. I wanted to know (and understand) if it would be enough to serialize one class which is holding other objects, or if all objects have to implement the serializable interface.

Hopefully I showed up the difference of my question to the one I got suggested by Ali Seyedi.

Answer 1

If you want it to work by just writing implements Serializable , then all of the classes will need to be Serializable , because otherwise an exception will be thrown when attempting to serialize the ArrayList .

You could avoid making movies and series Serializable by writing writeObject in such a way that instead of writing movies and series objects to the ObjectOutputStream , you write their fields directly. However, you should not adopt such an approach unless you have very good reason to do so.