JDK management is a real headache.

[sigeshuo]

The management of the JDK is quite chaotic—there’s a difference between the runtime JDK and the JDK that the project actually requires, and it's unclear how to configure them properly. It is recommended that the extension directly support selecting both the JDK used at runtime by the extension and the JDK needed for building or running the project. Please take a look at how JetBrains IDEA handles this; otherwise, the core JDK environment in the development setup will become very cumbersome to manage.

[rgrunber]

In most cases, users won't need to configure the runtime JRE/JDK as vscode-java ships with one for : win32-x64, darwin-x64, darwin-arm64, linux-x64, linux-arm64. Unless they explicitly choose the universal edition (which ships with no embedded JRE), or they currently wish to use javac as the underlying compiler (instead of ecj) which requires a Java 23 runtime for startup, there is java.jdt.ls.java.home to set a custom JRE for the actual extension.

As for configuring project JDKs, do you have https://marketplace.visualstudio.com/items?itemName=vscjava.vscode-java-pack installed ? It has a way to configure the project JDK : https://code.visualstudio.com/docs/java/java-project#_configure-runtime-for-projects .