Tester.java

java.util.ArrayList;
import javafx.geometry.Pos;
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.stage.Stage;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.scene.layout.Pane;
import javafx.scene.layout.HBox;
import javafx.scene.layout.GridPane;

public class Tester extends Application {
  static int first = 0;
  static boolean firstDone = false;
  static int second = 0;
  static int operation = 0;
  static int answer = 0;
  static boolean continuing = false;

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

  public void start(Stage primaryStage) {
    GridPane pane = new GridPane();
    Button one = new Button("1");
    Button two = new Button("2");
    Button three = new Button("3");
    Button four = new Button("4");
    Button five = new Button("5");
    Button six = new Button("6");
    Button seven = new Button("7");
    Button eight = new Button("8");
    Button nine = new Button("9");
    Button zero = new Button("0");
    Button add = new Button("+");
    Button subtract = new Button("-");
    Button multiply = new Button("x");
    Button divide = new Button("/");
    Button equals = new Button("=");
    Button clear = new Button("C");
    BtnHandler1 handler1 = new BtnHandler1();
    BtnHandler2 handler2 = new BtnHandler2();
    BtnHandler3 handler3 = new BtnHandler3();
    BtnHandler4 handler4 = new BtnHandler4();
    BtnHandler5 handler5 = new BtnHandler5();
    BtnHandler6 handler6 = new BtnHandler6();
    BtnHandler7 handler7 = new BtnHandler7();
    BtnHandler8 handler8 = new BtnHandler8();
    BtnHandler9 handler9 = new BtnHandler9();
    BtnHandler0 handler0 = new BtnHandler0();
    BtnHandlerPlus handlerPlus = new BtnHandlerPlus();
    BtnHandlerMinus handlerMinus = new BtnHandlerMinus();
    BtnHandlerTimes handlerTimes = new BtnHandlerTimes();
    BtnHandlerDivide handlerDivide = new BtnHandlerDivide();
    BtnHandlerEquals handlerEquals = new BtnHandlerEquals();
    BtnHandlerClear handlerClear = new BtnHandlerClear();
    one.setOnAction(handler1);
    two.setOnAction(handler2);
    three.setOnAction(handler3);
    four.setOnAction(handler4);
    five.setOnAction(handler5);
    six.setOnAction(handler6);
    seven.setOnAction(handler7);
    eight.setOnAction(handler8);
    nine.setOnAction(handler9);
    zero.setOnAction(handler0);
    add.setOnAction(handlerPlus);
    subtract.setOnAction(handlerMinus);
    multiply.setOnAction(handlerTimes);
    divide.setOnAction(handlerDivide);
    equals.setOnAction(handlerEquals);
    clear.setOnAction(handlerClear);
    pane.add(seven, 0, 0);
    pane.add(eight, 1, 0);
    pane.add(nine, 2, 0);
    pane.add(four, 0, 1);
    pane.add(five, 1, 1);
    pane.add(six, 2, 1);
    pane.add(one, 0, 2);
    pane.add(two, 1, 2);
    pane.add(three, 2, 2);
    pane.add(divide, 3, 0);
    pane.add(multiply, 3, 1);
    pane.add(add, 3, 2);
    pane.add(subtract, 3, 3);
    pane.add(equals, 2, 3);
    pane.add(clear, 0, 3);
    pane.add(zero, 1, 3);
    Scene scene = new Scene(pane);
    primaryStage.setScene(scene);
    primaryStage.show();
  }
}

class BtnHandler1 implements EventHandler<ActionEvent> {
  public void handle(ActionEvent e) {
    if (Tester.continuing) {
      Tester.first = 0;
      Tester.continuing = false;
      Tester.firstDone = false;
    }
    if (!Tester.firstDone)
      Tester.first = Tester.first * 10 + 1;
    else
      Tester.second = Tester.second * 10 + 1;
    System.out.print("1");
  }
}

class BtnHandler2 implements EventHandler<ActionEvent> {
  public void handle(ActionEvent e) {
    if (Tester.continuing) {
      Tester.first = 0;
      Tester.continuing = false;
      Tester.firstDone = false;
    }
    if (!Tester.firstDone)
      Tester.first = Tester.first * 10 + 2;
    else
      Tester.second = Tester.second * 10 + 2;
    System.out.print("2");
  }
}

class BtnHandler3 implements EventHandler<ActionEvent> {
  public void handle(ActionEvent e) {
    if (Tester.continuing) {
      Tester.first = 0;
      Tester.continuing = false;
      Tester.firstDone = false;
    }
    if (!Tester.firstDone)
      Tester.first = Tester.first * 10 + 3;
    else
      Tester.second = Tester.second * 10 + 3;
    System.out.print("3");
  }
}

class BtnHandler4 implements EventHandler<ActionEvent> {
  public void handle(ActionEvent e) {
    if (Tester.continuing) {
      Tester.first = 0;
      Tester.continuing = false;
      Tester.firstDone = false;
    }
    if (!Tester.firstDone)
      Tester.first = Tester.first * 10 + 4;
    else
      Tester.second = Tester.second * 10 + 4;
    System.out.print("4");
  }
}

class BtnHandler5 implements EventHandler<ActionEvent> {
  public void handle(ActionEvent e) {
    if (Tester.continuing) {
      Tester.first = 0;
      Tester.continuing = false;
      Tester.firstDone = false;
    }
    if (!Tester.firstDone)
      Tester.first = Tester.first * 10 + 5;
    else
      Tester.second = Tester.second * 10 + 5;
    System.out.print("5");
  }
}

class BtnHandler6 implements EventHandler<ActionEvent> {
  public void handle(ActionEvent e) {
    if (Tester.continuing) {
      Tester.first = 0;
      Tester.continuing = false;
      Tester.firstDone = false;
    }
    if (!Tester.firstDone)
      Tester.first = Tester.first * 10 + 6;
    else
      Tester.second = Tester.second * 10 + 6;
    System.out.print("6");
  }
}

class BtnHandler7 implements EventHandler<ActionEvent> {
  public void handle(ActionEvent e) {
    if (Tester.continuing) {
      Tester.first = 0;
      Tester.continuing = false;
      Tester.firstDone = false;
    }
    if (!Tester.firstDone)
      Tester.first = Tester.first * 10 + 7;
    else
      Tester.second = Tester.second * 10 + 7;
    System.out.print("7");
  }
}

class BtnHandler8 implements EventHandler<ActionEvent> {
  public void handle(ActionEvent e) {
    if (Tester.continuing) {
      Tester.first = 0;
      Tester.continuing = false;
      Tester.firstDone = false;
    }
    if (!Tester.firstDone)
      Tester.first = Tester.first * 10 + 8;
    else
      Tester.second = Tester.second * 10 + 8;
    System.out.print("8");
  }
}

class BtnHandler9 implements EventHandler<ActionEvent> {
  public void handle(ActionEvent e) {
    if (Tester.continuing) {
      Tester.first = 0;
      Tester.continuing = false;
      Tester.firstDone = false;
    }
    if (!Tester.firstDone)
      Tester.first = Tester.first * 10 + 9;
    else
      Tester.second = Tester.second * 10 + 9;
    System.out.print("9");
  }
}

class BtnHandler0 implements EventHandler<ActionEvent> {
  public void handle(ActionEvent e) {
    if (Tester.continuing) {
      Tester.first = 0;
      Tester.continuing = false;
      Tester.firstDone = false;
    }
    if (!Tester.firstDone)
      Tester.first = Tester.first * 10;
    else
      Tester.second = Tester.second * 10;
    System.out.print("0");
  }
}

class BtnHandlerPlus implements EventHandler<ActionEvent> {
  public void handle(ActionEvent e) {
    Tester.continuing = false;
    Tester.firstDone = true;
    Tester.operation = 1;
    System.out.println();
    System.out.println("+ ");
  }
}

class BtnHandlerMinus implements EventHandler<ActionEvent> {
  public void handle(ActionEvent e) {
    Tester.continuing = false;
    Tester.firstDone = true;
    Tester.operation = 2;
    System.out.println();
    System.out.println("- ");
  }
}

class BtnHandlerTimes implements EventHandler<ActionEvent> {
  public void handle(ActionEvent e) {
    Tester.continuing = false;
    Tester.firstDone = true;
    Tester.operation = 3;
    System.out.println();
    System.out.println("x ");
  }
}

class BtnHandlerDivide implements EventHandler<ActionEvent> {
  public void handle(ActionEvent e) {
    Tester.continuing = false;
    Tester.firstDone = true;
    Tester.operation = 4;
    System.out.println();
    System.out.println("/ ");
  }
}

class BtnHandlerEquals implements EventHandler<ActionEvent> {
  public void handle(ActionEvent e) {
    System.out.println();
    System.out.println("_____");
    if (Tester.operation == 1) {
      Tester.answer = Tester.first + Tester.second;
    } else if (Tester.operation == 2) {
      Tester.answer = Tester.first - Tester.second;
    } else if (Tester.operation == 3) {
      Tester.answer = Tester.first * Tester.second;
    } else if (Tester.operation == 4) {
      Tester.answer = Tester.first / Tester.second;
    }
    System.out.println(Tester.answer);
    System.out.println();
    System.out.println();
    Tester.first = Tester.answer;
    Tester.second = 0;
    Tester.continuing = true;
    Tester.firstDone = true;
  }
}

class BtnHandlerClear implements EventHandler<ActionEvent> {
  public void handle(ActionEvent e) {
    System.out.println();
    System.out.println();
    Tester.first = 0;
    Tester.second = 0;
    Tester.continuing = false;
    Tester.firstDone = false;
  }
}