Such diagrams always reflect the structure of actual classes and methods in your application. IntelliJ IDEA lets you generate a diagram on a package in your project. Open the Installed tab, find the Diagrams plugin, and select the checkbox next to the plugin name. Press Control+Alt+S to open the IDE settings and then select Plugins. If the relevant features aren't available, make sure that you didn't disable the plugin. This functionality relies on the Diagrams plugin, which is bundled and enabled in IntelliJ IDEA by default.
