Good luck, then. My next step is to install something later than Java 8 and start messing around.
(I went to install the new Eclipse version and it said "Can't find a JRE to use". Come on, I said, I've got six of them there. But it turned out that it wanted a 64-bit JRE and I had always been using 32-bit JREs. So fine, I downloaded and installed the 64-bit Java 8 and then it was happy.)
First big step was to re-install Eclipse-2020-03. I don't know if I didn't use the downloaded installer the first time but this time I made sure I did and 80% of my issues were solved right there.
Here are my ramblings of all the other stuff that I did, some of which are specific to my particular environment:
Was prompted with option to install Marketplace Client - did it
Used MPC to install Subclipse
Window > Preferences > Java > Compiler > Coompiler compliance level: 13 (won't go up to 14 yet)
Set environment variable:
This seems to be ignored and comes up as eclipse-oxygen\eclipse in class path variables (?)
Edited class path variables to be eclipse-2020-03
Ran one of my medium sized Swing projects. Everything seem to work fine.
Several projects showed errors and were listed under the "Problems" tab
Change environment variable
This is one of my own conventions that I have mixed feelings about. My pom.xml files use this as the
java version for a build. I have lots of pom.xml files and it was a pain keeping them in sync.
That clear up a number of project errors
Complains about Java-13 feature of text blocks (""")
Enabled it with quick fix in left margin
Caveate: IF you have project setting specifically designating Java-13 and you use Java-13 features, with this new
Eclipse and Java-14 plugin that won't work. You'll have to go into the project an upgrade it to 14 as well.