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From jdo-comm...@db.apache.org
Subject [Apache JDO Wiki] New: NewTypeSupport
Date Mon, 17 Jan 2005 16:28:18 GMT
   Date: 2005-01-17T08:28:18
   Editor: CraigRussell
   Wiki: Apache JDO Wiki
   Page: NewTypeSupport
   URL: http://wiki.apache.org/jdo/NewTypeSupport

   no comment

New Page:

= New Type Support =
This activity creates support for new types introduced into the Java language. For JDK 1.4,
three types that appear to be of interest were introduced: Currency, LinkedHashMap, and LinkedHashSet.

= General Issues =

 * New test cases need to be written for these classes. This is more work than it appears,
because we need to look at the existing RI tests and see which of these should be converted
to TCK tests. There are a number of tests that verify that adding and removing elements from
collections and adding and removing entries from maps result in the correct behavior. These
were never converted to TCK tests. So now is the time to take a careful look and make them
TCK tests. 

 * The classes are only available in JDK 1.4 and above. So we need a different strategy for
loading the support. Currently, the constructor of the ObjectTranscriber constructs the association
map between classes and the corresponding transcriber. The constructor must work regardless
of whether the classes are available in the environment. Probably we should define a new class
for the JDK 1.4 transcribers (ObjectTranscriber14Initializer) and another new class for JDK
1.5 transcribers (ObjectTranscriber15Initializer). These classes cannot contain static references
to the new classes; otherwise an ExceptionInInitializer will occur. It might be best to define
yet another class that can be called only if running in the appropriate environments. The
ObjectTranscriber can call these new classes, and the new classes can determine if the environment
is suitable. If not, they silently return. If they do have access to the classes, then they
can construct the transcriber instance and call back into the ObjectTranscriber with the new
class/transcriber map entry. This interface needs to be designed. Perhaps a new method on
ObjectTranscriber needs to be defined, but be careful because the ObjectTranscriber is in
its constructor. It might work to have the transcriber map be a static member that is initialized
to null in the initializer of ObjectTranscriber, is partially populated by the ObjectTranscriber
constructor, and is finished by the 14 and 15 initializers.

= Currency =

The strategy for Currency is to store the currency code persistently as a String. This can
be done in a CurrencyTranscriber in which the output sent to the stream is the result of calling
getCurrencyCode on the instance. Similarly, when reading an instance from the stream, the
static method Currency.newInstance(String) that takes the currency code can be called.

= LinkedHashMap =

The strategy for LinkedHashMap is similar to HashMap. 

= LinkedHashSet =

The strategy for LinkedHashSet is similar to HashSet. 

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