[jdom-interest] NoSuch*Exceptions in JDOM
Patrick.Dowler at nrc.ca
Fri Jun 16 10:31:21 PDT 2000
On Fri, 16 Jun 2000, Jools Enticknap wrote:
> It's a dichotomy, for NoSuchElementException to exist in this context
> because for an element not to have a child is perfectly reasonable, and
> it's not an exceptional condition. IMOHO.
All the arguments about which design entails the most code are not particularly
relevant. You have to be able to deal with the fact that a child isn't there,
and it has been shown that every method is about the same, codewise.
However, Jools has hit the nail on the head here: the standard use of
exceptions is to signal an error (typically in usage, such as invalid input
to a method, sometimes a programming error).
BTW, if getChild() were to return null on occasion, the people who like to
chain a bunch of getChild calls together can still do it:
attr = el.getChild("foo").getChild("bar").getAttribute("id");
// do something
catch (NullPointerException ex)
// ooops, one of the gets returned null
However, people who like to check for null can do it their way too. Since
a child might not exist, you have to check in any robust code. Returning
null is more consistent with standard Java style. For style, I look to
java.util.Map.get(Object key), which returns null if the key doesn't exist.
This is the most similar operation in the collections classes.
Canadian Astronomy Data Centre
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