Heh, righto. Are you familiar with Docker? Docker Hub is probably the best place to start. Assuming OpenJDK is OK for you, peruse the tags in the list - there are plenty of them depending on what you want/need - and swap them for the circleci/* image you are currently using.
For example, let’s say you want JDK 12 on Linux. I would guess 12-jdk is a good place to start, so you would use openjdk:12-jdk as your image name. So, using the Docker executor, your config would look a bit like this:
jobs:
build:
docker:
- image: openjdk:12-jdk
There may be some installed software that one would normally get in circleci/* images, in which case you would need to install that. I wonder, from that tag list, whether this image is based on Oracle Linux. That appears to use Yum as its package manager, which will let you install other things as required.