We discussed the servlet technology, a bit of JavaScript, HTML, and CSS. When programming in a real professional environment, these technologies are generally used. The creation of the user interface of applications, however, was not always based on these technologies. Older operating system-native GUI applications as well as Swing, AWT, and SWT use a different approach to create UI. They build up the UI facing the user from program code, and the UI is built as a hierarchical structure of components. When web programming started, Java developers had experience with technologies like these and projects created frameworks that tried to hide the web technology layer.

One technology worth mentioning is Google Web Toolkit, which implements the server as well as the browser code in Java, but since there is no Java environment implemented in the browsers, it transpiles (converts) the client part of the code from Java to JavaScript. The last release of the toolkit was created two...