javafx : Calculator example

1.Main.java

import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.stage.Stage;
import javafx.scene.Parent;
import javafx.scene.Scene;


public class Main extends Application {
	@Override
	public void start(Stage primaryStage) {
		try {
			Parent root = FXMLLoader.load(getClass().getResource("Main.fxml"));
			Scene scene = new Scene(root,300,300);
			scene.getStylesheets().add(getClass().getResource("application.css").toExternalForm());
			primaryStage.setScene(scene);
			primaryStage.setResizable(false);
			primaryStage.show();
		} catch(Exception e) {
			e.printStackTrace();
		}
	}
	
	public static void main(String[] args) {
		launch(args);
	}
}

2.Main.fxml

<?xml version="1.0" encoding="UTF-8"?>

<?import javafx.scene.control.Button?>
<?import javafx.scene.control.Label?>
<?import javafx.scene.layout.HBox?>
<?import javafx.scene.layout.StackPane?>
<?import javafx.scene.layout.VBox?>
<?import javafx.scene.text.Font?>

<VBox prefHeight="300.0" prefWidth="300.0" spacing="10.0" xmlns="http://javafx.com/javafx/9.0.1" xmlns:fx="http://javafx.com/fxml/1" fx:controller="application.MainController">
   <children>
      <StackPane prefHeight="50.0" prefWidth="200.0">
         <children>
            <Label fx:id="result" prefHeight="17.0" prefWidth="300.0">
               <font>
                  <Font name="System Bold" size="18.0" />
               </font>
            </Label>
         </children></StackPane>
      <HBox alignment="CENTER" prefHeight="50.0" prefWidth="300.0" spacing="10.0">
         <children>
            <Button mnemonicParsing="false" onAction="#processNumber" prefWidth="50.0" text="7">
               <font>
                  <Font size="18.0" />
               </font>
            </Button>
            <Button mnemonicParsing="false" onAction="#processNumber" prefWidth="50.0" text="8">
               <font>
                  <Font size="18.0" />
               </font>
            </Button>
            <Button mnemonicParsing="false" onAction="#processNumber" prefWidth="50.0" text="9">
               <font>
                  <Font size="18.0" />
               </font>
            </Button>
            <Button mnemonicParsing="false" onAction="#processOperator" prefWidth="50.0" text="/">
               <font>
                  <Font size="18.0" />
               </font>
            </Button>
         </children>
      </HBox>
      <HBox alignment="CENTER" prefHeight="50.0" prefWidth="300.0" spacing="10.0">
         <children>
            <Button mnemonicParsing="false" onAction="#processNumber" prefWidth="50.0" text="4">
               <font>
                  <Font size="18.0" />
               </font>
            </Button>
            <Button mnemonicParsing="false" onAction="#processNumber" prefWidth="50.0" text="5">
               <font>
                  <Font size="18.0" />
               </font>
            </Button>
            <Button mnemonicParsing="false" onAction="#processNumber" prefWidth="50.0" text="6">
               <font>
                  <Font size="18.0" />
               </font>
            </Button>
            <Button mnemonicParsing="false" onAction="#processOperator" prefWidth="50.0" text="*">
               <font>
                  <Font size="18.0" />
               </font>
            </Button>
         </children>
      </HBox>
      <HBox alignment="CENTER" prefHeight="50.0" prefWidth="300.0" spacing="10.0">
         <children>
            <Button mnemonicParsing="false" onAction="#processNumber" prefWidth="50.0" text="1">
               <font>
                  <Font size="18.0" />
               </font>
            </Button>
            <Button mnemonicParsing="false" onAction="#processNumber" prefWidth="50.0" text="2">
               <font>
                  <Font size="18.0" />
               </font>
            </Button>
            <Button mnemonicParsing="false" onAction="#processNumber" prefWidth="50.0" text="3">
               <font>
                  <Font size="18.0" />
               </font>
            </Button>
            <Button mnemonicParsing="false" onAction="#processOperator" prefWidth="50.0" text="-">
               <font>
                  <Font size="18.0" />
               </font>
            </Button>
         </children>
      </HBox>
      <HBox alignment="CENTER" prefHeight="50.0" prefWidth="300.0" spacing="10.0">
         <children>
            <Button mnemonicParsing="false" onAction="#processNumber" prefWidth="110.0" text="0">
               <font>
                  <Font size="18.0" />
               </font>
            </Button>
            <Button mnemonicParsing="false" onAction="#processOperator" prefWidth="50.0" text="=">
               <font>
                  <Font size="18.0" />
               </font>
            </Button>
            <Button mnemonicParsing="false" onAction="#processOperator" prefWidth="50.0" text="+">
               <font>
                  <Font size="18.0" />
               </font>
            </Button>
         </children>
      </HBox>
   </children>
</VBox>

3.Model.java

public class Model {
	public float calculate(long number1, long number2, String operator) {
		switch(operator) {
			case "+":
				return number1+number2;
			case "-":
				return number1-number2;
			case "*":
				return number1*number2;
			case "/":
				if(number2 == 0) {return 0;}
				else {return number1/number2;}
			default:
				return 0;
		}
	}
}

4.MainController.java

import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.scene.control.Label;
import javafx.scene.control.Button;

public class MainController {
	@FXML
	private Label result;
	private long number1 = 0;
	private String operator = "";
	private boolean start = true;
	private Model model = new Model();
	
	@FXML
	public void processNumber(ActionEvent event) {
		if(start) {
			result.setText("");
			start = false;
		}
		String value = ((Button)event.getSource()).getText();
		result.setText(result.getText() + value);
	}
	
	@FXML
	public void processOperator(ActionEvent event) {
		String value = ((Button)event.getSource()).getText();
		if(!value.equals("=")) {
			if(!operator.isEmpty()) {
				return;
			}
			else {
				operator = value;
				number1 = Long.parseLong(result.getText());
				result.setText("");
			}
		}
		else {
			if(operator.isEmpty()) {
				return;
			}
			else {
				long number2 = Long.parseLong(result.getText());
				float output = model.calculate(number2, number2, operator);
				result.setText(String.valueOf(output));
				operator = "";
				start = true;
			}
		}
	}
}