Newbie - I don't understand interface Serializable

[zalek]

The interface Serializable does not have any methods or variables.
If I create a subclass of an Object class - is this class
Serializable?
For example, let say I define:

public class A extends Object{
int a;
}

Now make the following definition:

public class A extends Object implements Serializable{
int a;
}

What makes the 2nd definition Serializable?

Thanks,

Zalek

 

[Lasse Reichstein Nielsen]

The interface Serializable does not have any methods or variables.

Correct. It's a "marker interface" which merely marks the class as being
intended for serialization. The serialization code checks for the marker,
and refuses to serialize something without it - not because it couldn't,
but just because it won't - serializing and derserializing something not
build for it could cause unexpected trouble.

Today it would probably have been implemented as an inherited
annotation.

If I create a subclass of an Object class - is this class
Serializable?

If it implements the Serializable interface.

For example, let say I define:

public class A extends Object{
int a;
}

Yes, that class isn't serializable. No need to write the "extends Object".
The class will automatically extend Object if no other superclass is
given.

Now make the following definition:

public class A extends Object implements Serializable{
int a;
}

What makes the 2nd definition Serializable?

That it implements the interface! That means that the default
serialization code will accept to serialize and deserialize objects
of that class.

/L

 

[zalek]

Correct. It's a "marker interface" which merely marks the class as being
intended for serialization. The serialization code checks for the marker,
and refuses to serialize something without it - not because it couldn't,
but just because it won't - serializing and derserializing something not
build for it could cause unexpected trouble.

Today it would probably have been implemented as an inherited
annotation.


If it implements the Serializable interface.



Yes, that class isn't serializable. No need to write the "extends Object".
The class will automatically extend Object if no other superclass is
given.




That it implements the interface! That means that the default
serialization code will accept to serialize and deserialize objects
of that class.

/L

Thanks!!!

Zalek

 

[Daniel Pitts]

Correct. It's a "marker interface" which merely marks the class as being
intended for serialization. The serialization code checks for the marker,
and refuses to serialize something without it - not because it couldn't,
but just because it won't - serializing and derserializing something not
build for it could cause unexpected trouble.

Today it would probably have been implemented as an inherited
annotation.

Actually, It has uses as a Type, but unfortunately the original
*ObjectStream API developers saw fit to accept "Object" instead of
Serializable.

 

[Lasse Reichstein Nielsen]

[Serializable]

Actually, It has uses as a Type, but unfortunately the original
*ObjectStream API developers saw fit to accept "Object" instead of
Serializable.

True, I have used Serializable for parameters to serialization helper
methods.

I would prefer it as an annotation, but I also want to add annotation
restrictions to parameters, e.g., something like:
void <T extends MyType & @MySerializable> doSomething(T param)

/L

 

[Mark Space]

The interface Serializable does not have any methods or variables.
If I create a subclass of an Object class - is this class
Serializable?

Lasse gave you some really good answers to your questions. Here's a
decent how-to on serialization from Sun. It explains further how
serialization actually works and gives some guidelines how to use it.

<http://java.sun.com/developer/technicalArticles/Programming/serialization/>

 

[Arne Vajhøj]

True, I have used Serializable for parameters to serialization helper
methods.

I would prefer it as an annotation, but I also want to add annotation
restrictions to parameters, e.g., something like:
void <T extends MyType & @MySerializable> doSomething(T param)

Annotations did not exist when Serializable was invented, so that
was not an option. And probably never will be an option either due
to compatibility.

..NET has it as an annotation (called attribute in .NET terminology).

BTW, if you want to restrict in template then I really think that
interface would fit best. To me restrictions are "is a".

Arne

 

[Roedy Green]

The interface Serializable does not have any methods or variables.
If I create a subclass of an Object class - is this class
Serializable?
For example, let say I define:

it is just marker to indicate you have thought through the class to do
the transients etc. needed to make it serialisable.

 

[Mike Schilling]

Lasse gave you some really good answers to your questions. Here's a
decent how-to on serialization from Sun. It explains further how
serialization actually works and gives some guidelines how to use
it.

<http://java.sun.com/developer/technicalArticles/Programming/serialization/>

And her is everything you'd ever want to know about serialization:
http://java.sun.com/j2se/1.3/docs/guide/serialization/spec/serialTOC.doc.html

 

[Arne Vajhøj]

And her is everything you'd ever want to know about serialization:
http://java.sun.com/j2se/1.3/docs/guide/serialization/spec/serialTOC.doc.html

I don't think it has changed, but:

http://java.sun.com/javase/6/docs/platform/serialization/spec/serialTOC.html

Arne

 

[Daniel Pitts]

[Serializable]

Actually, It has uses as a Type, but unfortunately the original
*ObjectStream API developers saw fit to accept "Object" instead of
Serializable.

True, I have used Serializable for parameters to serialization helper
methods.

I would prefer it as an annotation, but I also want to add annotation
restrictions to parameters, e.g., something like:
void <T extends MyType & @MySerializable> doSomething(T param)

/L

I think I would prefer a (more verbose but) more explicit syntax:

void <T extends @TypeAnnotatedWith(@MySerializable) MyType>
doSomething(T param)
but that's another story.