When I run  $ update-alternatives --config java  I get a few rows:  What is the difference between auto mode and manual mode?
Difference between auto mode and manual mode in update-alternatives
linux mint;alternatives
In a nutshell, update-alternatives:in Auto Mode, will select the generic name of the program automatically based on the Priority value of the alternatives; The one with the highest priority gets set as the generic name.in Manual Mode, will set the generic name as the user selected alternative irrespective of the Priority value of the alternatives, hence the name manual.Check this:% sudo update-alternatives --config editorThere are 5 choices for the alternative editor (providing /usr/bin/editor).  Selection    Path                Priority   Status------------------------------------------------------------  0            /bin/nano            40        auto mode  1            /bin/ed             -100       manual mode  2            /bin/nano            40        manual mode* 3            /usr/bin/emacs24     0         manual mode  4            /usr/bin/vim.basic   30        manual mode  5            /usr/bin/vim.tiny    10        manual modeNote that, /bin/nano is both available in auto and manual mode.If the link group were set in auto mode then the alternative with the highest priority i.e. /bin/nano (priority 40) would be selected as the generic name i.e. /usr/bin/editor. This is the default until the user introduces any change to the link group. On the other hand, in the manual mode, you can select any alternative as the generic name e.g. in the example, i have /usr/bin/emacs24 set as the generic /usr/bin/editor. You can select any one you like by using the Selection number on the left of the option.Now I can revert back from the manual mode to auto mode by selecting 0 from the above or by:sudo update-alternatives --auto editor