[jdom-interest] Request -- please allow all XML 1.1 conformant
text in Element.se tText()
chris at tech.com.au
Sun Mar 7 18:12:13 PST 2004
Elliotte Rusty Harold wrote:
> Have you read Meyer?
> If you have, you have severely misunderstood him at a very basic level.
> In Eiffel (and in Meyer's general philosophy of object oriented
> programming) "the invariants of all the parents of a class apply to
> the class itself" (OOSC, p. 570). In other words, an overriding method
> must satisfy the postconditions of the overridden method. This is
> trickier in Java than Eiffel because Java doesn't have inheritable
The fact that Java lacks a suitable class invariant and precondition
feature, does not alter the fact that Meyer's open-closed principle, and
his design of the Eiffel language is intended never to prevent
inheritance and redefinition of methods, provided of course you don't
violate the invariants and preconditions. If the invariant is something
along the lines of "this is a valid JDOM tree" then you are always free
to inherit and redefine a method so that you guarantee the invariant
using a different algorithm - e.g. because you KNOW it is valid because
of some other reason.
In other words - Yes - when you inherit you must conform to the
semantics of the original class, but No, you shouldn't be telling
somebody else when and how you must conform to your class. The fact that
Java lacks a proper method of forcing subclasses to conform does not
alter the fact that it is not your job to stop them inheriting and
> But even Eiffel also offers the ability to freeze a feature, roughly
> equivalent to Java's final.
Does it? I am only familiar with the compiler Freeze feature, which has
nothing to do with the language, and I can't find any "feature freeze".
But then again its a while since I programmed Eiffel.
> Meyer certainly does not recommend allowing subclasses unrestricted
> redefinition of superclass functionality, just the opposite in fact.
> Also, can you give a page cite for that quote? I couldn't find it.
It is not a citation from Meyer.
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