[jdom-interest] Announce: JDOMPlus a flexible XML framework f or Java

[James Strachan]

----- Original Message -----
From: "Jason Hunter" <jhunter at collab.net>
> I don't agree.  I think read-only trees have their place.  However, I
> lean toward having them implemented the same way Collections do, with
> facade classes.

Just being a pedant for a moment. Are you sure Collections use facade
classes?

To quote from http://rampages.onramp.net/~huston/dp/facade.html

"Facade ... provide a unified interface to a set of interfaces in a
subsystem. Facade defines a higher-level interface that makes the subsystem
easier to use."

"Facade defines a new interface, whereas Adapter uses an old interface.
Remember that Adapter makes two existing interfaces work together as opposed
to defining an entirely new one. [GOF, p219]"


(I don't have GOF to hand so am trusting this site for its facade
definition).

Java 2 Collections implement read only collections via alternate
implementations of the collections interfaces. There are singleton immutable
collections:-

    Collections.EMPTY_LIST;
    Collections.EMPTY_MAP;
    Collections.EMPTY_SET;

Each of these use private implementations of List, Map and Set which fully
implement their respective interfaces, they just throw
UnsupportedOperationException when someone attempts to change their value.

Also I could define my own read only List via

public FooList extends AbstractList {
    ...
}

and make it readonly via a similar mechanism.

Neither of these mechansims use different interfaces, they are just
implement the regular collection interfaces - so they aren't facades are
they?


<James/>


James Strachan
=============
email: james at metastuff.com
web: http://www.metastuff.com




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