Saturday, October 23, 2010

Java Pearls: case-insensitive Map?

Here's one more thing I did not know until very recently: how to get a Map with String keys that allows case-insensitive access? Or, case-insensitive membership checks. One typical use case is to handle case-insensitive entities such as names of HTML tags.

One obvious way to do this is to canonicalize keys by lower-casing (or upper-casing) keys both when inserted and when doing lookups. But this is actually not the only way to do this: there is a very simple JDK-provided alternative:

  Map<String,Object> tags = new TreeMap<String,Object>

and that's it; you can access values with any combination of casing. Similarly you can also create TreeSets for basic inclusion checks.

I hope this is something that most Java developers know and I had just somehow missed. But if not, here it is in case you happen to need such access.

ps. For what it's worth, the main reason I had missed this being a possibility was that I always thought comparator given to TreeMap and TreeSet would only be used for ordering. But thinking about it a bit more, this makes more sense; since comparisons must be done anyway (to find location of an entry to find or insert), why not use "equals" return value of comparator for something.

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