Quote:
Incompatible JVM - Version 1.8.0_271 of the JVM is not suitable for this product. Version: 11 or greater is required.
This is critical as the Eclipse 2020-09 codebase is compiled against Java 11. Seems you have solved this by installing or defaulting to a v11 or higher JRE.
With your JAVA_HOME variable set to a compatible v11+ JRE, Eclipse 2020-09, 2020-12, etc will work fine.
Quote:
Build path specifies execution environment JavaSE-1.8. There are no JREs installed in the workspace that are strictly compatible with this environment.
The compiler compliance specified is 1.8 but a JRE 15 is used.
This is merely a warning stating that the JRE visible to Eclipse JDT (i.e. the JRE/JDK being used to run/compile your code inside eclipse -
separate to the JRE that actually started up Eclipse since these are allowed to be different) is not a
"perfect match" for the build target version "1.8".
New JREs/JDKs generally have no problem running/compiling previous version binaries and in this case the message is saying you're using a v15 JRE/JDK environment to run code that has been tagged as v1.8.
You can either:
- Ignore this message
- Install a v1.8 JDK (openjdk, oracle, etc) to some folder then go to Window -> Preferences -> Java -> Installed JREs and add a reference to this v1.8 installation.
If you do take the second option, you should also go to
Window -> Preferences -> Java -> Installed JREs -> Execution Environments and mark the v1.8 installation as a "perfect match" under the JAVASE-1.8 environment.
Eclipse is quite flexible allowing you to install all versions of the JDK if you really wanted or needed to.
You can control which runtimes are used on a per project basis with:
Project -> Properties -> Java Build Path -> Libraries tab -> JRE System Library => Edit and set the project's execution environment.