Thanks, Storm Trooper.
Actionscript is used by Flash, and it's similar to JavaScript which is used by most browsers, as they're based on the same language standard.
There are some differences, mainly when it comes to manipulating graphics and audio, and each browser has slightly different JavaScript capabilities, but the differences here are minor.
Java is a very different language to JavaScript - while the syntax is very similar, Java is run in a "Virtual Machine", and I think it is usually compiled, whereas JavaScript is interpreted line by line at run time.