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Problem in Serialization

 
Sidharth Khattri
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Output is:
15


Static variables are Class variables and hence not serializable. But in the above program static instance t gets serialized. How?
 
E Armitage
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You are serializing and deserializing in the same program (same JVM) so the static variable will be shared among all instances in that program. Run the serialization and deserialization as separate programs.
 
Paweł Baczyński
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Serialization topic were removed from OCPJP 6
 
Sidharth Khattri
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Pawel Pawlowicz wrote:Serialization topic were removed from OCPJP 6


I saw a lot of questions on serialization on CertPal so I thought why not prepare it, as it can pop up on exam for few exam centers.

E Armitage wrote:You are serializing and deserializing in the same program (same JVM) so the static variable will be shared among all instances in that program. Run the serialization and deserialization as separate programs.


For that reason to check whether it's serialized or not, before serialization I changed t.i to 15 and after serialization I changed t.i to 17 and after deserialization t.i = 15 is returned, that means t is serialized as it returned the saved state of "i" when it was serialized. And running as separate programs also produces the same output, 15. Hence, it's serialized.
 
E Armitage
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Post what you tried and make sure you understand what static means. All objects of the class in the same value will always share it.
 
Sidharth Khattri
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E Armitage wrote:Post what you tried and make sure you understand what static means. All objects of the class in the same value will always share it.





I think I know what static means, though I can't understand what do you mean by this.
E Armitage wrote:All objects of the class in the same value will always share it.

 
E Armitage
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But you are checking the value of i and i is NOT static!

Also, what does the class A have to do with any of this?
 
Sidharth Khattri
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E Armitage wrote:But you are checking the value of i and i is NOT static!

Also, what does the class A have to do with any of this?


If t would not have been serialized, then the output would have been 11, default value of "i". But t here is serialized even though it's static, and output is 15.
Doing deserialization via different program ensure JVM does not remember the state of "i"(as you said in your previous post) but still it returns 15, so static "t" is serialized with i as 15.

I included class A to add static "a" in test class to check that static varaibles are not serialized, but still static "t" is getting serialized.
 
Sidharth Khattri
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Output:
15
5

You see? static "a" is not serialized, so even after changing its "x" from 5 to 7, upon deserialization "tt.a.z" returns 5, it's default value.
So how can static "t" get serialized?
 
E Armitage
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You are probably confusing yourself because you have two test objects one inside the other. Create a separate class with just the main method to clear things somewhat.
 
Sidharth Khattri
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E Armitage wrote:You are probably confusing yourself because you have two test objects one inside the other. Create a separate class with just the main method to clear things somewhat.


Can you please explain what are you saying? Because from what I understand, static "t" is getting serialized. If not, what code would you write to justify it?
 
Astha Sharma
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I tried some codes which shows that if you save a static variable as a part of the object, it doesn't gets serialized, but if you pass static variable directly to the method writeObject(), it get's stored to the file. Because you are not writing the object itself to the file, instead you are writing the contents of that object to the file.



prints output - 11
static test object declared at line1 didn't get serialized with the test object.
 
Sidharth Khattri
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Astha Sharma wrote:I tried some codes which shows that if you save a static variable as a part of the object, it doesn't gets serialized, but if you pass static variable directly to the method writeObject(), it get's stored to the file. Because you are not writing the object itself to the file, instead you are writing the contents of that object to the file.



prints output - 11
static test object declared at line1 didn't get serialized with the test object.


But in AnotherClass's serializeTest() method you declared t again:

which basically is a "new" test instance that'll have 11 as the default value of i. You are serializing a different "t" instance and not the "t" from test class that has i = 15;
That is why your output is 11.

Any more suggestions or any idea how is the static instance serialized here?
 
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