What is serialVersionUID?

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RC - 29 Jun 2005 13:24 GMT

import javax.servlet.*;
import javax.servlet.http.*;

public class MyClass extends HttpServlet {
....
}

warning: [serial] serializable class MyClass has no definition of
^
serialVersionUID
public class MyClass extends HttpServlet {

What is this warning message mean?
How do I get rid it?

Thank Q very much in advance!

P.S. I know a warning message is NOT an error, but
someday, sometime may be cause run time failure.

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Ingo R. Homann - 29 Jun 2005 13:52 GMT

Hi,

> import javax.servlet.*;
> import javax.servlet.http.*;
[quoted text clipped - 9 lines]
>
> What is this warning message mean?

You need a serialVersionId, if your class implements "Serializable".
HttpServlet does so, and so you need such an id. (It is used, if the
Servlet-Context is relaunched and your sessions should be made
persistant / restored. If you do not need this feature, you do not need
a serialVersionId.)

> How do I get rid it?

There is some switch to disable the warning (e.g. in Eclipse...)

> P.S. I know a warning message is NOT an error, but
> someday, sometime may be cause run time failure.

Yes, its better not to ignore warnings (although that's not possible
with Java5 :-()

Ciao,
ingo

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blaine@worldweb.com - 29 Jun 2005 15:41 GMT

You'll need to add a serialVersionUID to your class eg:

public class MyClass extends HttpServlet{
public static final long serialVersionUID = 1L;

public MyClass(){
}
}

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Skip - 29 Jun 2005 15:53 GMT

> You'll need to add a serialVersionUID to your class eg:
>
[quoted text clipped - 4 lines]
> }
> }

That static field may be private too.

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Bryce - 29 Jun 2005 16:06 GMT

>Hi,
>
[quoted text clipped - 27 lines]
>Yes, its better not to ignore warnings (although that's not possible
>with Java5 :-()

Added note:

If you are using Eclipse, it can generate the id for you. Click on the
yellow lightbulb.

--
now with more cowbell

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Roedy Green - 30 Jun 2005 07:23 GMT

>serialVersionUID

see http://mindprod.com/jgloss/serialization.html

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Roedy Green - 29 Aug 2005 08:13 GMT

>serialVersionUID
>public class MyClass extends HttpServlet {
>
>What is this warning message mean?
>How do I get rid it?

see http://mindprod.com/jgloss/serialization.html

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http://mindprod.com Again taking new Java programming contracts.

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What is serialVersionUID?

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