Java and JavaScript might look like one was a direct descendant of the other, but in reality they are far from that.
Java is an object oriented programming language developed by Sun Microsystems that is capable of running on multiple operating systems with the use of an interpreter.
JavaScript, on the other hand, was created by Netscape as a scripting language much like a client side version PHP. It cannot create stand alone applications, but instead resides on an internet browser.
Java uses its own code then executes it on a virtual machine that interprets the Java code into its counterpart native code.
JavaScript is a scripting language, and as such it isn’t compiled. A JavaScript enabled browser takes the script and process it, it would then execute the instructions on the script. The main use of JavaScript is to provide a level of interactivity to web pages that are not achievable with simple HTML.
It can be used along with other technologies like AJAX to give an even more interactive experience. JavaScript can also interact with elements that are not from within its code which Java doesn’t do. Java applications can only be embedded into html pages and from that point on, the Java application works on its own.
Java and JavaScript are two very different languages, because of that they also have different requirements in order to function properly. Installing Java support in your browser does not mean that it would also be able to support JavaScript applications and vice versa.