Why dependency on both default-jre and java<N>-runtime

[Carnë Draug <carandraug+dev@gmail.com>]

Hi

I was going through the pkg-java policy and found this [1]:

    Programs must depend on the needed runtime environment
    (default-jre or default-jre-headless if need a GUI or not, and
    java<N>-runtime or java<N>-runtime-headless as provided by
    alternative Java environments).

However, java<N>-runtime packages are virtual packages provided by
default-jre so I don't understand why.  Could anyone clarify?

Thank you
Carnë

[1] https://www.debian.org/doc/packaging-manuals/java-policy/x105.html