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   Re: SAX2: DTDDeclHandler (minimalist position)

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  • From: Elliotte Rusty Harold <elharo@metalab.unc.edu>
  • To: "Bill la Forge" <b.laforge@jxml.com>, <xml-dev@ic.ac.uk>
  • Date: Fri, 2 Apr 1999 12:31:00 -0500

At 10:57 AM -0500 3/31/99, Bill la Forge wrote:
>From: Elliotte Rusty Harold <elharo@metalab.unc.edu>
>>>Using objects for constants can also cause problems with persistent
>>>data, if you were depending on a singularity and testing with ==.
>>This isn't a problem with the syntax I've described because there is only a
>>fixed set of objects in which identity comparisons are the same as equality
>How do you maintain singularities when deserializing a JavaBean which
>contains a reference to one of these objects?
>That is to say, you have a constant which references an object. No problem.
>Now you have a bean with a variable which has been assigned the constant
>value. No problem.
>Now you save the bean. No problem.
>Now you deserialize the bean. No problem.
>Now you test the value of the variable in the bean with ==. Woops. The test
>always returns false.

You can use custom readObject() and writeObject() methods to keep
singletons single if necessary.  I discuss this very example (with a
different singleton) in Chapter 11 of Java I/O.

| Elliotte Rusty Harold | elharo@metalab.unc.edu | Writer/Programmer |
|        XML: Extensible Markup Language (IDG Books 1998)            |
|   http://www.amazon.com/exec/obidos/ISBN=0764531999/cafeaulaitA/   |
|  Read Cafe au Lait for Java News:  http://sunsite.unc.edu/javafaq/ |
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