Wednesday, August 20, 2008

From the "things I wish Java had" file...

Often you'll find yourself writing code similar to the following:
String childName = root.getChild().getName();
Now, if root.getChild() returns null, you'll get a dreaded NullPointerException. There are a couple ways to guard against this of course, but they're fairly verbose. You could check each traversal point for null...
String childName = null;
Node child = root.getChild();
if (child != null) {
childName = child.getName();
}
That works, but it gets messy quickly if you have another traversal or two (and yes, I know, excessive depth is a bad code smell).

Alternatively, you could do something like this:
String childName = null;
try {
childName = root.getChild().getName();
} catch(NullPointerException ignored) {
}
But you could really end up littering your code with ignored catch blocks.

Ideally, I would love to have a method of saying "traverse as far as you can, but return null if you encounter null along the way". Perhaps a special operator?
String childName = root,getChild(),getName();
Anyway, I'm sure there are languages out there that support this notion. It's high on my list of desired features for an alternative to Java!

5 comments:

David Dossot said...

Check Groovy safe navigation idiom, you will love it.

I tend to use Groovy scripts now for this kind of unsafe operations: since Java6 it is now so easy to access scripting from a standard Java application.

Carl Schmidt said...

That's exactly what I want, thanks! I've gotten so behind on things, am definitely looking forward to catching up...

Anonymous said...

Old blog, I know, but you could always write a wrapper for that behavior. It's not optimal either, but it would be the least cutterful way of doing it.

I just wish there was a destructor in Java. There's a lot of things destructors can do other than releasing memory :(

Freya West said...

The word 'Idioms', in this context, should be taken to mean something like 'Common Practice'. This page isn't an appropriate place to put patterns, it's a place to put example of common solutions to java coding problems. If the Idiom linked to off this page has no code, then its a pattern. If its about using a related group of classes to solve a design problem, then it is a pattern too.

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