IntelliJ IDEA

tl;dr

/Users/your_username_here/Library/Java/JavaVirtualMachines/

Choose File > Project Structure > Platform Settings > SDKs

You can inspect the JDKs known to IntelliJ by choosing File > Project Structure > Platform Settings > SDKs.

Notice how the location of the selected JDK is shown in the JDK home path field.

In this example, the JDK downloaded by IntelliJ was put in:

/Users/your_username_here/Library/Java/JavaVirtualMachines/

Note that this location contrasts with the location used by some of the independent JDK installers. In my experience, those tools use the root /Library path, rather than in the user’s ~/Library. That full path would be: /Library/Java/JavaVirtualMachines.

SDKMAN!

By the way, an alternative tool I prefer for finding, downloading, installing, and uninstalling JDKs (and other software kits like Gradle) is SDKMAN!. It is a command-line tool for Unix-like operating systems including macOS.

This setting is changed in the "Structure for New Projects" dialog. Navigate to "File" -> "New Projects Setup" -> "Structure..."

Next, modify the "Project SDK" and "Project Language Level" as appropriate.

Previous versions of IntelliJ IDEA had this setting in "File" -> "Other Settings" -> "Default Project Structure...".

IntelliJ IDEA 12 had this setting in "Template Project Structure..." instead of "Default Project Structure..."