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At 10:57 AM -0500 3/31/99, Bill la Forge wrote: >From: Elliotte Rusty Harold <elharo@m...> >>>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 >>comparisons. > > >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@m... | 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/ | | Read Cafe con Leche for XML News: http://sunsite.unc.edu/xml/ | +----------------------------------+---------------------------------+ xml-dev: A list for W3C XML Developers. To post, mailto:xml-dev@i... Archived as: http://www.lists.ic.ac.uk/hypermail/xml-dev/ and on CD-ROM/ISBN 981-02-3594-1 To (un)subscribe, mailto:majordomo@i... the following message; (un)subscribe xml-dev To subscribe to the digests, mailto:majordomo@i... the following message; subscribe xml-dev-digest List coordinator, Henry Rzepa (mailto:rzepa@i...)
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