Java installed?

I have Nextcloud installed on a RPI3 with this image “”.
No problems with this.
I want to add Nextant to my system. To do this I need to know wether Java is running and if it is in which version. My command

java -version

results in

-bash: java: command not found

What is wrong with this?

Most likely reason: you don’t have java installed.

Thank you.
If i enter at the bash “whereis java” i get "java: /usr/share/java"
if i then enter this directory and ask again “java -version” I get again "-bash: java: command not found"
if i enter “ls” I get “libintl.jar” in red.
I don’t know what this means, but it seems to me that Java is indeed not installed.
Is this normal/common?