Install libopenjfx-java-doc by entering the following commands in the terminal:
sudo apt update sudo apt install libopenjfx-java-doc
JavaFX/OpenJFX 8 - Rich client application platform for Java (Javadoc)
JavaFX/OpenJFX is a set of graphics and media APIs that enables Java developers to design, create, test, debug, and deploy rich client applications that operate consistently across diverse platforms. . This package contains the API documentation for libopenjfx-java.