It looked like I had my default JDK set to the old Java 8 home (running these commands in Terminal.app)...
Terminal
% java -version
java version "1.8.0_231"
Java(TM) SE Runtime Environment (build 1.8.0_231-b11)
Java HotSpot(TM) 64-Bit Server VM (build 25.231-b11, mixed mode)
% grep "export JAVA_HOME" .zprofile
.zprofile:export JAVA_HOME=`/usr/libexec/java_home -v 1.8`
So what I did first was remove that export line from the ~/.zprofile script. Then using the java_home utility, I was able to list all of the java installations that I had...
Terminal
% /usr/libexec/java_home -V
Matching Java Virtual Machines (4):
14.0.1, x86_64: "Java SE 14.0.1" /Library/Java/JavaVirtualMachines/jdk-14.0.1.jdk/Contents/Home
11.0.7, x86_64: "Java SE 11.0.7" /Library/Java/JavaVirtualMachines/jdk-11.0.7.jdk/Contents/Home
9.0.4, x86_64: "Java SE 9.0.4" /Library/Java/JavaVirtualMachines/jdk-9.0.4.jdk/Contents/Home
1.8.0_231, x86_64: "Java SE 8" /Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home
That's quite a few! (also I didn't know that some of these were even installed!)
Using the Terminal.app again, I was able to simply delete the JDKs that I didn't want installed by using the rm command and passing in the Home directory of the JDK to delete (using sudo of course, and entering your admin user password), for example...
Terminal
sudo rm -rf /Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk
I proceeded to delete all but the latest JDK using this method. There was nothing else to do after this, the JDK was simply gone!
-i