Switching Boot JDK
RubyMine already has a bundled boot JDK to start with. You can install and use any other JDK, version 1.8 or higher.
To switch the IDE boot JDK
On the main menu, chooseor press Ctrl+Shift+A.
In the list of actions that appears, find Switch IDE boot JDK action and select it. Simplify your search by typing the first letters:
In the dialog that opens, select the desired JDK:
Click OK to apply changes.