[ubuntu] Need Java help!!

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http://ubuntuforums.org – I want to download Youtube videos, and whenever I try one method, I need Java installed. I've done various methods using Terminal, and I've now got the latest version... I think. I'm new to Ubuntu, and I have no real idea what the hell I am doing, (but fun so far!), and I need help to install/download/configure/ work some wizardry to get Java running. If there are alternative methods to download Youtube videos, I would like to know about them too. Any help is appreciated, thanks! (Hardware)