Since Sun’s API search is a real pain in the arse and even DocWeb doesn’t allow you to quickly search the Java API, this firefox plugin is a substantial improvement: https://addons.mozilla.org/en-US/firefox/addon/60675/

It basically redirects the search query to Google’s “I’m Feeling Lucky” feature to search Java’s API for the class information.

Together with Second Search querying the Java API is now lightning fast: https://addons.mozilla.org/en-US/firefox/addon/4096/