Re: class loading issue when super class has reference to sub class

[Craig L Russell]

Hi Ilan,

On Jun 24, 2006, at 4:32 PM, Ilan Kirsh wrote:

Hi Erik,

I remember similar problems with this enhanced method in the past
so I just checked your test with ObjectDB, but now it works well
with no exception.


at enhancement time. Hopefully this change should do the difference.

The code that is produced by the ObjectDB Enhancer is slightly different and instead of jdoFieldNames.length there is a constant that is calculated

The spec requires:

protected static int jdoGetManagedFieldCount();

the enhanced class.

The sample code for Employee in section 21.21 is:

21.21.7 Generated jdoGetManagedFieldCount

loading of the subclasses.
The implementation for topmost classes in the hierarchy:
protected static int jdoGetManagedFieldCount () {
return jdoFieldNames.length;
}
The implementation for subclasses:
protected static int jdoGetManagedFieldCount () {
return <pc-superclass>.jdoGetManagedFieldCount() +
jdoFieldNames.length;
}



Craig

Please note that there is a difference between what the spec requires in terms of the semantics and what the sample code shows as an implementation. The sample code in 21.21 is not normative. This method returns the number of managed fields declared by this class plus the number inherited from all superclasses. This method is generated in the class to allow the class to determine at runtime the number of inherited fields, without having introspection code in The generated method returns the number of managed fields in this class plus the number of inherited managed fields. This method is expected to be executed only during class So it looks like we could improve the example code by replacing the jdoFieldNames.length with an unnamed constant (which does not require that the jdoFieldNames field be initialized).

Regards,

Ilan

----- Original Message ----- From: "Erik Bengtson" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>; <jdo-dev@db.apache.org>
Sent: Saturday, June 24, 2006 11:15 PM

Subject: class loading issue when super class has reference to sub class

Hi,


sub class


public class Aclass {
private Cclass cclass;
}
public class Bclass extends Aclass {
}

public class Cclass extends Bclass {
}

public class Main {
public static void main(String[] args) throws Exception {
//The following line throws ExceptionInInitializerError caused by
java.lang.NullPointerException
System.out.println(Class.forName("org.jpox.test.Bclass"));
}
}


Exception in thread "main" java.lang.ExceptionInInitializerError
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at org.jpox.test.Aclass.___jdo$loadClass(Aclass.java)
at org.jpox.test.Aclass.__jdoFieldTypesInit(Aclass.java)
at org.jpox.test.Aclass.<clinit>(Aclass.java)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at org.jpox.test.Main.main(Main.java:6)
Caused by: java.lang.NullPointerException
at org.jpox.test.Bclass.jdoGetManagedFieldCount(Bclass.java)
at org.jpox.test.Cclass.__jdoGetInheritedFieldCount(Cclass.java)
at org.jpox.test.Cclass.<clinit>(Cclass.java)
... 8 more


See for a diagram
http://www.jpox.org/servlet/jira/browse/ENHANCER-58


The issue is due to the implementation of the jdoGetManagedFieldCount

The implementation for topmost classes in the hierarchy:
protected static int jdoGetManagedFieldCount () {
return jdoFieldNames.length;
}
The implementation for subclasses:
protected static int jdoGetManagedFieldCount () {
return <pc-superclass>.jdoGetManagedFieldCount() +
jdoFieldNames.length;
}

There is an issue when initialising a class when super class has reference to (Cclass extending Bclass extending Aclass and Aclass has a reference to Cclass)

Craig Russell
Architect, Sun Java Enterprise System http://java.sun.com/products/jdo
408 276-5638 mailto:[EMAIL PROTECTED]
P.S. A good JDO? O, Gasp!

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