JavaFX menu item show shortcuts on right hand side

You can add an accelerator key in scene builder or add it directly in the fxml file like so

<?import javafx.scene.input.*?>
...
<MenuItem mnemonicParsing="true" onAction="#mnuSaveAction" text="%menu.title.save" fx:id="mnuSave">
   <accelerator>
      <KeyCodeCombination alt="UP" code="S" control="DOWN" meta="UP" shift="UP" shortcut="UP" />
   </accelerator>
</MenuItem>

KeyCodeCombination has two constructors, second example:

<MenuItem text="Renommer..."      onAction="#rename" mnemonicParsing="true">
   <accelerator>
      <KeyCodeCombination code="F2"><modifiers></modifiers></KeyCodeCombination>
   </accelerator>
</MenuItem>

If by "in javafx" you mean without using fxml you can use mnuSave.setAccelerator(KeyCombination);

If your are not using fxml file then you can add key combination like below.

MenuItem gotoLine = new MenuItem("Goto");
KeyCombination gotoKeyCombination = new KeyCodeCombination(KeyCode.G, KeyCombination.CONTROL_DOWN);
gotoLine.setAccelerator(gotoKeyCombination);
gotoLine.setOnAction(event -> {
            System.out.println("CTRL+G event triggered");
            System.out.println(event.toString());
 });