JavaFX: Aplicación Zodiaco

Main.java

import javafx.application.Application;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.geometry.Insets;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.control.TextField;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

public class Main extends Application {

    public static void main(String[] args) {
        launch(args);
    }

    @Override
    public void start(Stage primaryStage) throws Exception {

        TextField dia = new TextField();
        dia.setPromptText("Día");

        TextField mes = new TextField();
        mes.setPromptText("Mes");

        Label mensaje = new Label("Este es un mensaje");

        Button boton1 = new Button("Calcular");
        boton1.setOnAction(new EventHandler<ActionEvent>() {
            @Override
            public void handle(ActionEvent event) {
                int miDia = Integer.parseInt(dia.getText());
                int miMes = Integer.parseInt(mes.getText());
                String signo = obtenerSigno(miDia, miMes);
                mensaje.setText("Su signo es: " + signo);
            }
        });

        VBox caja = new VBox();
        caja.getChildren().add(dia);
        caja.getChildren().add(mes);
        caja.getChildren().add(boton1);
        caja.getChildren().add(mensaje);

        caja.setSpacing(15);
        caja.setPadding(new Insets(20, 20, 20, 20));

        Scene scene = new Scene(caja, 300, 200);

        primaryStage.setScene(scene);
        primaryStage.setTitle("Zodiaco");
        primaryStage.show();
    }

    public static String obtenerSigno(int dia, int mes) {
        String signo = "";
        switch (mes) {
            case 1:
                if (dia > 21) {
                    signo = "ACUARIO";
                } else {
                    signo = "CAPRICORNIO";
                }
                break;
            case 2:
                if (dia > 19) {
                    signo = "PISCIS";
                } else {
                    signo = "ACUARIO";
                }
                break;
            case 3:
                if (dia > 20) {
                    signo = "ARIES";
                } else {
                    signo = "PISCIS";
                }
                break;
            case 4:
                if (dia > 20) {
                    signo = "TAURO";
                } else {
                    signo = "ARIES";
                }
                break;
            case 5:
                if (dia > 21) {
                    signo = "GEMINIS";
                } else {
                    signo = "TAURO";
                }
                break;
            case 6:
                if (dia > 20) {
                    signo = "CANCER";
                } else {
                    signo = "GEMINIS";
                }
                break;
            case 7:
                if (dia > 22) {
                    signo = "LEO";
                } else {
                    signo = "CANCER";
                }
                break;
            case 8:
                if (dia > 21) {
                    signo = "VIRGO";
                } else {
                    signo = "LEO";
                }
                break;
            case 9:
                if (dia > 22) {
                    signo = "LIBRA";
                } else {
                    signo = "VIRGO";
                }
                break;
            case 10:
                if (dia > 22) {
                    signo = "ESCORPION";
                } else {
                    signo = "LIBRA";
                }
                break;
            case 11:
                if (dia > 21) {
                    signo = "SAGITARIO";
                } else {
                    signo = "ESCORPION";
                }
                break;
            case 12:
                if (dia > 21) {
                    signo = "CAPRICORNIO";
                } else {
                    signo = "SAGITARIO";
                }
                break;
        }
        return signo;
    }

}