The short answer
Usually, after a check. Might hold something you care about. Look inside before removing it.
What is it?
JDKs downloaded from inside IntelliJ IDEA or Android Studio (Project Structure › SDKs › Download JDK) are installed per user in ~/Library/Java/JavaVirtualMachines. JDKs installed with an official installer go to /Library/Java/JavaVirtualMachines instead. Each one typically takes 200 to 400 MB.
JDKs installed by IntelliJ or Android Studio. Keep the versions your projects use.
What happens if you delete it?
The IDE can download the same JDK again in a minute, but nothing does it automatically. Projects configured to use a removed JDK show an error until you pick another one.
How to remove it properly
Run /usr/libexec/java_home -V in Terminal to list the installed JDKs, check which ones your projects use (Project Structure › SDKs in the IDE), then quit the IDE and move the unused .jdk folders to the Trash.
Quit the app that uses it, then move it to the Trash. Empty the Trash when you’re sure.
How MoreRoom helps
MoreRoom recognises this item and labels it “Review first”: it shows what’s inside, its size and last use, so you can decide. Nothing is removed without your say, and everything goes to the Trash first, with Undo.
Frequently asked questions
Can I delete JDKs in ~/Library/Java/JavaVirtualMachines?
Usually, after a check. Might hold something you care about. Look inside before removing it. The IDE can download the same JDK again in a minute, but nothing does it automatically. Projects configured to use a removed JDK show an error until you pick another one.
Will Java JDKs (user) come back after I delete it?
Yes. The IDE can download the same JDK again in a minute, but nothing does it automatically. Projects configured to use a removed JDK show an error until you pick another one.
How do I remove Java JDKs (user) properly?
Run /usr/libexec/java_home -V in Terminal to list the installed JDKs, check which ones your projects use (Project Structure › SDKs in the IDE), then quit the IDE and move the unused .jdk folders to the Trash.