import javafx.fxml.FXML;
import javafx.scene.control.ListView;
import javafx.scene.input.MouseButton;
import javafx.scene.input.MouseEvent;

public class UserController {

  @FXML
  private ListView<String> userList;

  @FXML
  private void onListDoubleClick(MouseEvent e)  {    
    if(
        e.getButton().equals(MouseButton.PRIMARY) && 
        e.getClickCount() == 2) {
      System.out.println("Kattintott elem: " + 
      userList.getSelectionModel().getSelectedItem());
    }
  }
}