But say, working for jagex, wouldn't they look at programmers who can program java, as runescape is a Java based game? (sorry for being a noob)
Also, is RuneScape written in Java or JavaScript? (I hear its different?)
Generally if you were working on game code for Jagex, sure, you would probably want to know Java.
This brings me back to my point that a language doesn't make a programmer though: once you understand different programming paradigms and concepts, and understand generally the advantages and caveats of each programming language, it doesn't really matter which one you learn. I could probably learn a new language in a couple to a few weeks if I wanted to because I in general understand the different paradigms, technologies, and I don't just randomly learn a language without knowing what it does.
A good programmer will know many languages and use each respective one for each respective situation. You can specialise in a particular language, however generally speaking that is severely limiting your job opportunities. As an example, you can do web development in PHP, but you can also do it in Python. Which would you choose? Well, the answer depends on what you're doing and how you're doing it.
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RuneScape is indeed written in Java. Not JavaScript.
JavaScript is a scripting language that is implemented in to a webpage. It is not a language for building programs (technically I wouldn't even call it programming, but scripting). Your webbrowser will load up a page and if you have JavaScript enabled (which most people do) the browser will run the JavaScript code, which can load up different information and tell the webbrowser how to display certain things. Of course, there are other uses for it, but in general that's what it tends to do.
For example, if you write a reply on this forum, you'll notice that there's a text editor that's a bit more than just a textbox. If you click the Bold button, the BBCode for bolding your text will appear. If you click on a smiley, it will insert a smiley and so on. This text editor is made possible by JavaScript.
JAVA on the other hand is an actual programming language for the development of (you guessed it) actual programs. You can implement Java apps in to a webpage, certainly, however Java apps are basically just like regular desktop applications that are fed in to your browser. You can also use Java to make desktop applications and mobile apps. All in all it's a very useful language, but for any serious game development I consider it pretty limited.
Mobile games etc. can be developed in Java, and if you have enough time, experience, a team of coders and a fuckload of cash, yeah, you can make something like RuneScape in Java. However, you will notice that most other desktop games, for example World of Warcraft, Crysis, Battlefield, Starcraft, so on so forth have nothing to do with Java because there are better options available for making those sorts of games.
... Which brings me back to my point of knowing multiple languages: in the gaming industry it will make you a hell of a lot more employable.