The IntelliJ function has a function that can display Javadoc on the Web, so just set it on the Oracle Web page. The location is the location of the SDKs in the module settings of the project.
URL of each version of Javadoc https://docs.oracle.com/javase/jp/8/docs/api/ https://docs.oracle.com/javase/jp/11/docs/api/
However, with the default settings of IntelliJ, Javadoc is not displayed automatically, so separate settings are required.
However, Javadoc is not displayed by auto-complete of input such as dots. Valid only when autocomplete is activated with * Ctrl (cmd) + space *.
It can be set to start with one button.