Calculator.java~

import java.util.Stack;
import javafx.application.Application;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.TextField;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.GridPane;
import javafx.stage.Stage;


public class Calculator extends Application{
    
    //the calculator dimensions
    public static int CALC_WIDTH = 400;
    public static int CALC_HEIGHT = 300;
    
    //adding opereator and operand data members
    private Stack<Double> operandStack = new Stack<>();
    private Stack<Operator> operatorStack = new Stack<>();
    
    //holds the current number being built from the press of the button
    private String currentNumber = "";
    
    //the calculator screen
    private TextField screen;
    
    //the calculator buttons
    private Button button1;
    private Button button2;
    private Button button3;
    private Button button4;
    private Button button5;
    private Button button6;
    
    /**
     * This method will append digits to the number that is being built from the number presses
     * **/
    private void appendDigit(String digit){
        //add digit to the number
        currentNumber += digit;
        screen.setText(currentNumber);
    }
    
    public static void main(String[] args){
        launch(args);
    }
    
    @Override
    public void start(Stage primaryStage){
        //create calculator screen
        screen = new TextField();
        
        //creating buttons
        button1 = new Button("1");
        button2 = new Button("2");
        button3 = new Button("3");
        button4 = new Button("4");
        button5 = new Button("+");
        button6 = new Button("=");
   
        
        //attach handler to process clicks
        ButtonHandler handler = new ButtonHandler();
        button1.setOnAction(handler);
        button2.setOnAction(handler);
        button3.setOnAction(handler);
        button4.setOnAction(handler);
        button5.setOnAction(handler);
        button6.setOnAction(handler);
        
        //set up a grid panel for the keyboard
        GridPane keypad = new GridPane();
        keypad.setMinSize(CALC_WIDTH, CALC_HEIGHT);
        //keypad.setPadding(new Insets(10, 10, 10, 10));
        //keypad.setVGap(5);
        //keypad.setHGap(5);
        keypad.setAlignment(Pos.CENTER);
        
        //attach the buttons to the keypad grid
        //have different columns and rows for each button
        keypad.add(button1, 0, 0);
        keypad.add(button2, 1, 0);
        keypad.add(button3, 0, 1);
        keypad.add(button4, 1, 1);
        keypad.add(button5, 2, 0);
        keypad.add(button6, 2, 1);
        
        
        //put screen and keypad together
        BorderPane gui = new BorderPane();
        gui.setTop(screen);
        gui.setCenter(keypad);
        
        //set up the scene
        Scene scene = new Scene(gui);
        primaryStage.setTitle("Calculator");
        primaryStage.setScene(scene);
        primaryStage.show();
        
    }
    
    //handler for processing the button clicks
    private class ButtonHandler implements EventHandler<ActionEvent>{
        
        /**
         * we are going to add number buttons here
         * we are going to call appenddigit method to build the number from the buttons being pressed
         */ 
        
        @Override
        public void handle(ActionEvent e){
            if(e.getSource() == button1){
                appendDigit("1");
            }
            else if(e.getSource() == button2){
                appendDigit("2");
            }
            else if(e.getSource() == button3){
                appendDigit("3");
            }
            else if(e.getSource() == button4){
                appendDigit("4");
            }
            else if(e.getSource() == button5){
                appendDigit("+");
            }
            else if(e.getSource() == button6){
                appendDigit("=");
            }
            
}
    }
}