How to open two Javafx windows?

I'm using javafx, want to write a code in 'setOnAction' of a button to close a javafx1 class an run javafx2 class, but i've seen error 'Application launch must not be called more than once'. How can i fix this?

//This code is in the class JavaFX1:
button.setOnAction(new EventHandler<ActionEvent>() {
      @Override
      public void handle(ActionEvent event) {
          JavaFX2.main(null); //How can i change current line?
          stage.close();
      }
});

It's done like this:

        @Override
        public void handle(ActionEvent event) {
            System.out.println("Hello World!");

            Stage secondStage = new Stage();
            secondStage.setScene(new Scene(new HBox(4, new Label("Second window"))));
            secondStage.show();

        }

You may also set coordinates and size of the new window.