Overriding serialization -- and the defaul - java help on CodeGym

The readObject() method of ObjectInputStream has a type: it returns Object. Therefore, I find it easy to understand the following example code used in the deserialization:

Cat newCat = (Cat) objectinputstream.readObject();

However, in the task-2015, we used the objectinputstream.defaultReadObject() method, which is void. It returns nothing. It reads the object, the data is already in the stream - but I don't understand the continuation of what more it does. I've been thinking a lot, if this method doesn't return anything, how can I pass the scanned object to the new Thread() constructor? I had to look at the downloaded correct solution, and there I found this:

private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
     in.defaultReadObject();
     runner = new Thread(this);
     runner.start();
}

The question arises: how does this work? Perhaps the defaultReadObject() method automatically sets the fields of the current Solution object to the read value? (Perhaps in some hidden way, hidden in the background.) And how can this code be used usefully, e.g. if I want to start the loading of the object from main() ? For example: Solution sol = new Solution.readObject() ? Thank you in advance!:)

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Lisa

Level 41

8 December 2021, 08:59

solution

There is even more you should wonder. Like readObject being private and not overridden. So how can any class outside of the serialized class access it in the first place. The reason you probably know already as CG mentions it all the time. This is done using reflection. So when ObjectInputStream.readObject is called it looks (using reflection) for a method private readObject... in the object to deserialize. If it is there it makes it accessible. Then it checks if it should execute default deserialization (defaultReadObject()) or if deserializeation is done by hand (load the objects you want). Both (ObjectInputStream.readObject and Solution.readObject) methods are connected using the reflection mechanism, don't forget that. That way ObjectInputStream knows about what you deserialize. So you could (instead of default deserialization) just load the speed

speed = in.readInt();

That meachanism is useful for the case handled here and for singletons Don't be mad with me... ahh, no 😜🤪🧐

Gellert Varga

Level 23 , Szekesfehervar, Hungary

8 December 2021, 23:20

Thanks for the explanation! This is the first time I've heard of reflection. But now I understand a little bit how this code works.:)

Overriding serialization -- and the defaultReadObject() method