Because of different versions of java are installed, you can change default option with this command.

sudo update-alternatives --config java

With this command, you can select java version as default option.

Full control of the software: You build the package from a source you can see and read. You decide which features you want to build in and which aren't needed. You can choose build options, optimisation and whatever else fancy stuff you want modified. With a binary distribution this simply isn't possible. | Portage's emerge is powerful: Portage is a package management system with a huge amount of options and features. | Fully customizable: The usage of advanced features like USE flags makes it more customizable than any binary distribution. | Freedom: You are free to do whatever you want with it. As a result, its configuration reflects your unique taste and personality. | Not beginner-friendly: You have to read a lot of instructions to start, even if you are familiar with Linux. Furthermore, as you have to configure the kernel and init system, expect some boot failures at beginning. | Great for anyone who is serious about learning the intricacies of Linux: It's useful for both beginners and professionals. For the installation, Gentoo offers various types, which are referred to as stages. Basically meaning how in depth you would want to go into the process of installation. For beginners it's useful to choose for a starting distro due to its various stages that can be very time consuming but beneficial as you learn the composition in general of Linux. | Can by optimized to any given CPU by using proper compile flags: Since everything is being built on your PC you can fine-tune the code to make use of your CPU. And all it requires is two lines of string variables in a global config. | Portability: There are many architectures available for Gentoo : i386, x86-64, PowerPC, PowerPC 64, sparc, DEC Alpha, ARM, MIPS, PA-RISC, S390, IA-64, sh, m68k. | Can be officially systemd-free: Gentoo's default init system is OpenRC. Gentoo also officially supports systemd-free Gnome and udev. Users are free to choose any init system they want. | Documentation and community are second to none: Provides a whole handbook to refer to during setup and usage. | A very large collection of software is available: There are more than 19.000 packages available in the official repository. And even more with overlays. | Since everything must be compiled it takes a lot longer to update: And if you have to update the kernel or some heavy software like Chromium it can takes hours if not more on weaker hardware. | Gentoo does not impose a standard look-and-feel | No default installer: Installation must be done manually by following instructions in the handbook. | Superiority and smartness: You get superiority and get called smart daily for going through the processes of punishing yourself to a compile install you also get a cool neofetch logo. | Live USB installation: Installation via a Live USB allows you to go back and fix mistakes from it without having to restart the whole installation process. | Customized package installation can take a long time and cause installation failures: The Gentoo package management system allows you to configure what compilation flags packages should support - i.e. specific processor flag support (SSE, SSE2, etc.), -O1, -O2, -O3 optimization, etc. · If you accept one of the default flags, Gentoo downloads binaries from the server. However, if you decide to optimise, it can and will download all source packages and start compiling allthe programs and libraries on your system. If your chosen flags don't work with a particular library, installation will fail. | Somewhat outdated solutions: While being outdated per se is virtually impossible for a rolling-release distro with a large community, a large portion of said community sticks to outdated solutions. For example, Gentoo's primary init system is OpenRC, which is cumbersome and awkward to use and provides little control over the system. While you can just choose systemd, it will require some tinkering. Other examples include stubbornly declaring an initramfs a last resort and an "oh my god 1337 H4XX0RZ surely have nothing better to do than trying for a month to exploit some vulnerability to steal my pony art, I have to fortify so hard my performance and ease of use will suffer" 90s security mentality. · Because of just how much freedom Gentoo provides you with, this usually isn't a big deal though. | Too hard | Has no live images with graphical interface: Full installation is hand-made with a CLI (Command-Line Interface)

To include man page(s) and mvnDebug command within the alternative, just add slave options like this:

INSTALL_HOME="/opt/maven/apache-maven-3.5.0"

sudo update-alternatives --install "/usr/bin/mvn" "mvn" "${INSTALL_HOME}/bin/mvn" 100 \
  --slave "/usr/bin/mvnDebug" "mvnDebug" "${INSTALL_HOME}/bin/mvnDebug" \
  --slave "/usr/share/man/man1/mvn.1.gz" "mvn.1.gz" "${INSTALL_HOME}/man/mvn.1.gz" \
  --slave "/usr/share/man/man1/mvnDebug.1.gz" "mvnDebug.1.gz" "${INSTALL_HOME}/man/mvnDebug.1.gz"

Hint: If your download did not include man pages, you can use help2man to generate mvn.1.gz and then symlink mvnDebug.1.gz to it.

cd ${INSTALL_HOME}/man
ln -s mvn.1.gz mvnDebug.1.gz

Arch is rolling release, and things are guaranteed to work only if they are all the most recent version. This is why partial upgrades are not supported .