Master Oogways enlighten us about Optional in his previous two sessions, and Now he set the stage for the final advise on Optional and believe me that is the most searchable questions on the internet about Optional, also many peoples mailed in OpenJDK forum regarding “Why Optional is not Serializable?” , Oogways promises to PO that he will try to give the best possible answers and we all keen to know the answer from Oogways as he is the wisest master in the world.
Let see the conversation happened beet ween PO an Oogways.
PO: Master I try to figure out why Optional is not serializable also searched on the internet but not found any compelling answers can you please enlighten me?
Master gives a calm look to Po and start his speech
Oogways: Before starting why Optional is not serializable I want to talk about an upcoming project in jdk10 which is Project Valhalla.
Project Valhalla: The slogan of project Valhalla is “Codes like a class, works like an int!” — so, project Valhalla try to create a new user-defined datatype which can be treated as class i.e you can have data and behaviours tied into this but when that datatype runs on JVM it will act as primitives , i.e this datatype not stored in heap memory unlike Object and it does not have reference it will act as primitives like int, float — it will stores in the stack memory. So obvious question comes
what are the benefits of that new datatype?
To answer this question we have to know a concept of ValueObject– In Java sometimes we design some Objects which just carry value do nothing else– act on the value, or preserve the state, this Object does not have any identity think about Integer what it does it wraps a primitive int value and why it is created?– Just to support
java collection framework, It just a Wrapper Object, think about the ValueObject pattern in JEE or a Money Object(Value and currency), these are used to pass values so conceptually these objects are not a proper object by definition, those objects are immutable in nature , and two objects are equals if their values are equal no identity check and obviously does not preserve a state which is the crux of an Object it acts as primitives more than Object so we called the Value Object, Now we all know there is cost associate to create Object, Even to make an Integer from int , it has to create a header(8-16 byte) and reference(4-8 bytes) in case of a reachable object, so instead of 4 bytes it takes 4+8+4=16 bytes minimum. also in case of the array of Integers, it has to traverse through pointers to fetch value as Integer array stores the references, not the value but in case of primitives it will store value locally in the stack so traversing is very fast, So the concept Project Valhalla it treats value type as primitives it gives us to create user-defined primitives.
Now I will tell you something about serialization.
Serialization: Serialization is a technique by which one can store the Object state in form of the stream so in future, we can reconstruct the state of the Object in same or another JVM from the stream. To achieve serialization is not a problem but Serialization has a huge maintenance cost, Because when we make an Object serializable we have to take care of the following
Back and forward JVM support: The Key feature of a serialization is it would be supported across any versions of Java including current and future release, so if an Object serializes in Java8 should be deserialized in java1.4 and vice versa so it supports backward and forward compatibility.So it has huge maintenance cost as various scenarios can occur where it may be broken, think about a situation if you want to add a new HAS-A relationship in your serializable Object and that class has been introduced in upper version of JDK how it would be deserialized in lower JVM as lower JVM does not know about that class. Also in case deserializing it needs back-references to reconstruct the graph and need the Object reference. So Serialization hindering further modification of the Object, so maintaining Serialization is not a cup of tea.
Now, I come to the point why the Optional is not serializable, PO, If you look about the Optional it just wraps a value so it is a boxed class, If two Optional value is same we can say those are equals, so it treats like a Value type even in JavaDoc of Optional says
“This is a value-based class; use of identity-sensitive operations (including reference equality (
==), identity hash code, or synchronization) on instances of
Optional may have unpredictable results and should be avoided.”
so it is clear Optional is a Value type and they know the Project Valhalla is in roadmap so obviously, they want to change Optional to a Value type (Identityless) when Project Valhalla onboard. And if they make them Serializable, now it needs to reside in heap memory and to deserialize the same need a reference but Project Valhalla remove them from heap and stores in the stack so the question is how you deal with the same. there are lots of If and buts so they don’t confident enough to make it serializable.
Another thing is the motto of Serialization is to reconstruct the state but Optional is a Valuetype and stateless so why they make it serializable it does not meet the criteria of serialization. Those are the reasons to not makeOptional serializable.
PO : I understood the Objective of not making Optional serializable but if they make it value type and make it serializable both by following technique, Suppose they make Optional as value type so it does not have any reference, but in the case of de-serialization we can box them in an Object and make it present on heap memory, so it will be dubious nature, by default it is a value type but in case of deserialization it will act as an Object, by this we can solve the problem.
Oogways: PO, I like your thought, it proves that why I choose you as a Dragon Warrior. Really it is a compelling idea but think Optional is a Value type and in case of deserialization you want to make footprint in heap at that point it breaks the purpose of value type, To support serialization we unnecessary breaks the principle of project Valhalla, and bring back the problem which project Valhalla tries to solve, Optional is the category of Value Object to make it dubious nature to just support serialization is just a lame idea to me, To carrying the cost of serialization should have a compelling use cases, I don’t see anything comelling in case of Optional.
PO: I understood master, Thanks for giving me a new direction I will learn more about project Valhalla and value type.
Oogway: Well, I am planning to give a session on Project Valhalla, you can attend that session.
PO: yes Master, I will and I bring my friend Shamik with me.
Oogways nodded his head.