A Java JavaScript developer designs, implements, and maintains software applications using both Java and JavaScript languages. They employ Java for server-side development to manage the logic of the system, database interactions, and user authorization. JavaScript, on the other hand, is used for client-side scripting to create interactive web pages, validate user input, and enhance user experience. They ensure the smooth integration of both languages for seamless operation. Their responsibilities also include debugging, code testing, and software optimization, along with adhering to coding standards and keeping up with the latest industry trends for continuous improvement.