I have been a long time Debian (Ubuntu, elementary, Bodhi, Linux Mint) user and transitioned to Arch (Manjaro XFCE) about a year ago.
Most of the software that I had used in Debian are available in Manjaro's repositories (can be installed using pacman). The remaining are almost always available in AUR (Arch User Repository).
If you prefer GUI, then Pamac is the default tool in Manjaro XFCE and it does a better job than Ubuntu's app center and package managers.
On doing a quick search in Pamac, I found that Oracle JDK 6-10 is available in AUR. Note: You may have to enable AUR from Pamac's settings before using it. Netbeans 10.0 is available in Manjaro's repository (doesn't need AUR).
From my experience, 85% of the commands are the same for Arch family. 5-10% of the commands are desktop specific. So if you are staying within KDE 90-95% of the commands will be the same.
The most notable difference is in commands of installing/uninstalling the software.
To install in Ubuntu,
sudo apt-get install netbeans
To install in Manjaro,
sudo pacman -S netbeans
To uninstall in Ubuntu,
sudo apt-get remove netbeans
To uninstall in Manjaro,
sudo pacman -R netbeans
Debian VS Arch CLI
Easy to use
I found Manjaro to be more easy to use than Ubuntu thanks to Pamac and AUR.
Make a live USB for Manjaro KDE, test the OS by booting from that USB and then decide if it suits you or not. While testing from your live USB, your installed OS and files will not be affected at all. If all goes well, you can install Manjaro KDE from that same live USB.