In the first form, REPOSITORY will just be appended to /etc/apt/sources.list. In the second form, ppa:/ will be expanded to the full deb line of the PPA and added into a new file in the /etc/apt/sources.list.d/ directory. The GPG public key of the newly added PPA will also be downloaded and added to apt's keyring.

Apr 01, 2017 Ubuntu Linux Remove / Delete PPAs apt-get command Oct 07, 2019 How To Delete A Repository And GPG Key In Ubuntu - OSTechNix Jul 06, 2019

Jun 08, 2019

Jun 08, 2019 Ubuntu Manpage: add-apt-repository - Adds a repository add-apt-repository is a script which adds an external APT repository to either /etc/apt/sources.list or a file in /etc/apt/sources.list.d/ or removes an already existing repository. The options Powered by the Ubuntu Manpage Repository, file bugs in Launchpad UBUNTU PACKAGES FOR R

java - How to install JDK 11 under Ubuntu? - Stack Overflow

Installing/Linux/Ubuntu – Deluge Jun 08, 2019 Ubuntu Manpage: add-apt-repository - Adds a repository