IntelliJ IDEA jump from interface to implementing class in Java

In addition to Ctrl + Alt + B mentioned above, you can also use the mouse: Ctrl + Alt + LeftMouseButton to jump directly to implementations.

Yes, On mac, it is Command + Option + B. You will need to move your cursor to the interface name before invoking the shortcut. I'm not sure what's the shortcut in PC, for if you right click the interface name -> "Go To" -> "Implementations"... the shortcut is listed there.

In Windows, it is CTRL + ALT + B: JetBrains navigation documentation.