apt-get purge oracle-java8-jdk installed openjdk 1.7 and removed other packages

On Ubuntu 14.04 I did

sudo apt-get purge oracle-java8-jdk

and not only was the jdk8 removed but openjdk7 was installed. JDK7 wasn't shown in the options given by

sudo update-alteatives --config java

before the purge.

The apt-get purge also removed a couple of other packages which we create in house.

Why did apt-get purge install openjdk7? Is this to satisfy some dependencies that apt-get knows about?

Would the custom packages that were removed have been removed because they had a dependency on oracle-java8-jdk?

Thanks