Java is the leading language in the industry today, and with Oracle ADF we have a great offering for developer looking to be more productive leveraging Java on the Oracle platform. But there are other languages in the market too, and JavaScript is quickly gaining popularity and by many accounts is the second most popular language today. JavaScript is very popular for front end development of web interfaces. ADF and JET target completely different audiences. Below table clarifies differences between these 2 frameworks.
Advanced ADF and Webcenter Learning