Again, thank you for helping me out!
We have a winner.
java -version
openjdk version "1.8.0_181"
OpenJDK Runtime Environment (Zulu 8.31.1.122-linux_aarch32hf) (build 1.8.0_181-b122)
OpenJDK Client VM (Zulu 8.31.1.122-linux_aarch32hf) (build 25.181-b122, mixed mode, Evaluation)
I actually noticed that the 64-bit was wrong; removed it, including the links, and installed the 32-bit soft float package, which didn’t work either; but this one ‘hard float’ does.
To summarise the steps, which worked for me based on your post:
sudo mkdir /opt/jdk/
cd /opt/jdk
sudo wget http://cdn.azul.com/zulu-embedded/bin/zulu8.31.1.122-jdk1.8.0_181-linux_aarch32hf.tar.gz
sudo tar -xzvf zulu8.31.1.122-jdk1.8.0_181-linux_aarch32hf.tar.gz
sudo update-alternatives --install /usr/bin/java java /opt/jdk/zulu8.31.1.122-jdk1.8.0_181-linux_aarch32hf/bin/java 181
sudo update-alternatives --install /usr/bin/javac javac /opt/jdk/zulu8.31.1.122-jdk1.8.0_181-linux_aarch32hf/bin/javac 181
sudo rm zulu8.31.1.122-jdk1.8.0_181-linux_aarch32hf.tar.gz
sudo apt purge zulu-embedded-8
java -version