implement serializable in java api class

[Lando Chan]

I want to save a sequence object and since it does not implement Serializable I try some code below but it failed. I wonder what I miss.

[Prasad Saya]

See this Oracle's Java tutorial on extending a class: https://docs.oracle.com/javase/tutorial/java/IandI/subclasses.html

[Tony Docherty]

Not sure why you are saving the state of the object but if you are trying to provide persistent storage then I would advise against using Serializable. if, on the other hand, you are implementing transient storage then Serializable is an acceptable approach, you do need a no args constructor though to deserialise an object.
An alternative approach to extending the Sequence class would be to create a wrapper class which implements the readObject and writeObject methods as stated in the API docs for Serializable. The wrapper class could then handle serialization and deserialization of the Sequence object's state through these methods.

[Dave Tolls]

With respect to extending Sequence, from the docs for Serializable:

To allow subtypes of non-serializable classes to be serialized, the subtype may assume responsibility for saving and restoring the state of the supertype's coderanch, protected, and (if accessible) package fields. The subtype may assume this responsibility only if the class it extends has an accessible no-arg constructor to initialize the class's state. It is an error to declare a class Serializable if this is not the case. The error will be detected at runtime.

Sequence does not hav a no-args constructor, so cannot be serialized at all.

[Tony Docherty]

Dave Tolls wrote:Sequence does not hav a no-args constructor, so cannot be serialized at all.

You can serialize it using the alternate approach I described in my earlier post provided there are getters and setters for the fields you need to serialize (or you are willing to use reflection).

[Lando Chan]

I want to save the Sequence object so that I can restore it and play the music I have created. So it is impossible to do that ?

[Lando Chan]

Okey, I just read the last two replies that it is unserializable. Thank you very much

[Rob Spoor]

You can probably still serialize it, but you need to use some more advanced techniques like a serialization proxy. In short, instead of serializing instances of your Sequencer sub class, you serialize a replacement (writeReplace). In turn, this replacement will return a newly created instance of your sub class when it's deserialized (readResolve). This way you can call any constructor you want, as long as you have its values.

[Rob Spoor]

FYI, you can use this to even return something completely different. An example is EnumSet. This has two implementations depending on the number of constants in the enum (RegularEnumSet for <= 64 elements, JumboEnumSet for > 64 elements). The serialization proxy simply stores the elements in the set. Upon deserializing, the proxy uses the EnumSet constructs to make sure the correct type is picked. That means that you can serialize an EnumSet when the enum has <= 64 constants (so it's a RegularEnumSet), and deserialize it when the enum has > 64 constants (because you added some). It then automatically becomes a JumboEnumSet.