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Serialize/Deserialize Java enum

Theodore David Williams
Ranch Hand

Joined: Dec 21, 2009
Posts: 102
After two days I finally figured out why (i think) my enum class is not getting deserialzed properly.


Now lets say that I programatically set the length and width and serialize to a file.


If I close my application and try to deserialize, or deserialize from a different application I lose the length and width settings.

My question is this: Is there a way that I can write custom serialize/deserialze code to prevent this behavioir? I.E. override writeObject and readObject? If I can how would I do that?

Thanks in advance!
Martin Vanyavchich
Ranch Hand

Joined: Sep 16, 2008
Posts: 241
Hope this dosen't sound too silly, but shouldn't your enum implement Serializable?


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Theodore David Williams
Ranch Hand

Joined: Dec 21, 2009
Posts: 102
It can, but java enums already implement Serializable not no need to re-implement.

From the Java Serialization Spec:

Enum constants are serialized differently than ordinary serializable or externalizable objects. The serialized form of an enum constant consists solely of its name; field values of the constant are not transmitted. To serialize an enum constant, ObjectOutputStream writes the string returned by the constant's name method. Like other serializable or externalizable objects, enum constants can function as the targets of back references appearing subsequently in the serialization stream. The process by which enum constants are serialized cannot be customized; any class-specific writeObject and writeReplace methods defined by enum types are ignored during serialization. Similarly, any serialPersistentFields or serialVersionUID field declarations are also ignored--all enum types have a fixed serialVersionUID of 0L.


Is there any way to achieve the behavior I want???
David Newton
Author
Rancher

Joined: Sep 29, 2008
Posts: 12617

Not according to your quote.
Rob Spoor
Sheriff

Joined: Oct 27, 2005
Posts: 19541
    
  16

Correct. readObject is also not possible since java.lang.Enum implements that to throw an exception. Any attempt to implement this method yourself will fail.

To be honest, I think your design is flawed. Modifiable enums? Really?


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Theodore David Williams
Ranch Hand

Joined: Dec 21, 2009
Posts: 102
Rob,

You are correct my design is flawed.

I think what I really wanted after thinking about it is something like this (which works nicely)
Rob Spoor
Sheriff

Joined: Oct 27, 2005
Posts: 19541
    
  16

I'd make the inner enum public, or it will only be visible from the same package. Unless that's what you want of course.
Vineet Manohar
Greenhorn

Joined: Mar 25, 2010
Posts: 2
I agree with moving the setter out of Enums, as enums are supposed to be constants. You should not change them once they are created.

As far as serialization is concerned, you should be careful how you serialize the enum value to a database or disk. You should not use the cardinal value or the constant literal to serialize. Use a business value, which is unlikely to change. e.g. "one", "two" in the above example. If interested see my article 3 ways to serialize Java Enums
Towid Khan
Greenhorn

Joined: Apr 12, 2008
Posts: 8
et al

Enums are automatically serializable and comparable.

here are couple of suggestions that you might want to try out

1. initialize the length and width in the constructor rather than setting them afterwards
2. make the enum public and possibly put it in a different .java file?? -> Good Practice. saves lots valuable time in human lives while figuring out " ?? why ?? "

Regards,
TK
Paul Draper
Greenhorn

Joined: Feb 02, 2013
Posts: 1
Theodore David Williams wrote:Rob,

You are correct my design is flawed.

I think what I really wanted after thinking about it is something like this (which works nicely)


What you really want is a class with a private constructor and three static instances of that class, ONE, TWO, or THREE

Then serialize those, and reset them during deserialization. No need to cram Enum into something it was never meant to do or be.
 
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