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serializable

Shyam Hai
Ranch Hand

Joined: Feb 04, 2009
Posts: 68
Now i got this warning.

Warning : "The serializable class DizleeServlet does not declare a static final serialVersionUID field of type long"

What is the reason...
Rob Spoor
Sheriff

Joined: Oct 27, 2005
Posts: 19790
    
  20

You've set your IDE (Eclipse, Netbeans, etc) to warn you if you miss the serial version UID.
http://www.javapractices.com/topic/TopicAction.do?Id=45
http://java.sun.com/javase/6/docs/api/java/io/Serializable.html

From the latter:
The serialization runtime associates with each serializable class a version number, called a serialVersionUID, which is used during deserialization to verify that the sender and receiver of a serialized object have loaded classes for that object that are compatible with respect to serialization. If the receiver has loaded a class for the object that has a different serialVersionUID than that of the corresponding sender's class, then deserialization will result in an InvalidClassException. A serializable class can declare its own serialVersionUID explicitly by declaring a field named "serialVersionUID" that must be static, final, and of type long:

ANY-ACCESS-MODIFIER static final long serialVersionUID = 42L;

If a serializable class does not explicitly declare a serialVersionUID, then the serialization runtime will calculate a default serialVersionUID value for that class based on various aspects of the class, as described in the Java(TM) Object Serialization Specification. However, it is strongly recommended that all serializable classes explicitly declare serialVersionUID values, since the default serialVersionUID computation is highly sensitive to class details that may vary depending on compiler implementations, and can thus result in unexpected InvalidClassExceptions during deserialization. Therefore, to guarantee a consistent serialVersionUID value across different java compiler implementations, a serializable class must declare an explicit serialVersionUID value. It is also strongly advised that explicit serialVersionUID declarations use the private modifier where possible, since such declarations apply only to the immediately declaring class--serialVersionUID fields are not useful as inherited members. Array classes cannot declare an explicit serialVersionUID, so they always have the default computed value, but the requirement for matching serialVersionUID values is waived for array classes.

If you don't know how to create a proper serialVersionUID, you can use the serialver tool, or make your IDE create one for you.


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Campbell Ritchie
Sheriff

Joined: Oct 13, 2005
Posts: 40052
    
  28
That is an Eclipse error message.

Right-click the little yellow triangle, and you get a drop-down list of options, including "default SUID" and "create SUID".
Campbell Ritchie
Sheriff

Joined: Oct 13, 2005
Posts: 40052
    
  28
I made a mistake: Don't right-click the yellow triangle, but left-click it.
Muhammad Khojaye
Ranch Hand

Joined: Apr 12, 2009
Posts: 449

Ragavendran Sivaji Rao wrote:Now i got this warning.

Warning : "The serializable class DizleeServlet does not declare a static final serialVersionUID field of type long"

What is the reason...



http://java.dzone.com/articles/dont-ignore-serialversionuid


http://muhammadkhojaye.blogspot.com/
 
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subject: serializable