This homework has one problem which with java FX GUI and event handling. Eclipse

Question

This homework has one problem which with java FX GUI and event handling. Eclipse Reminder Create a JavaFX Project Choose: File, Never, other, JavaFX, JavaFXProject. Supply a project name, e.g. hw6_Flastname Choose: Finish Expand the files in the package Explorer, You will see the following items that were automatically created: An application package. A main class which is where you will write your code. A file named application.css which is a (empty) style sheet. This is a very powerful and useful technique for styling your GUI; however, we will not use it. A JavaFX SDK folder and a build file, build fx build neither of which we will use Open main class and write your code there.

Explanation / Answer

Working fine code..

import javafx.application.Application;
import javafx.beans.binding.Bindings;
import javafx.beans.property.*;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.*;
import javafx.scene.input.KeyEvent;
import javafx.scene.layout.*;
import javafx.stage.Stage;
import javafx.stage.StageStyle;

import java.util.HashMap;
import java.util.Map;

// a simple JavaFX simple_Calculator.
public class simple_Calc extends Application {
private static final String[][] TMPLATE = {
{ "7", "8", "9", "/" },
{ "4", "5", "6", "*" },
{ "1", "2", "3", "-" },
{ "0", "c", "=", "+" }
};

private final Map<String, Button> accltrs = new HashMap<>();

private DoubleProperty stackValue = new SimpleDoubleProperty();
private DoubleProperty value = new SimpleDoubleProperty();

private enum Op { NOOP, ADD, SUBTRACT, MULTIPLY, DIVIDE }

private Op curOp = Op.NOOP;
private Op stackOp = Op.NOOP;

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

@Override public void start(Stage stage) {
final TextField screen = createScreen();
final TilePane buttons = createButtons();

stage.setTitle("simple_Calc");
stage.initStyle(StageStyle.UTILITY);
stage.setResizable(false);
stage.setScene(new Scene(createLayout(screen, buttons)));
stage.show();
}

private VBox createLayout(TextField screen, TilePane buttons) {
final VBox layout = new VBox(20);
layout.setAlignment(Pos.CENTER);
layout.setStyle("-fx-background-color: chocolate; -fx-padding: 20; -fx-font-size: 20;");
layout.getChildren().setAll(screen, buttons);
handleaccltrs(layout);
screen.prefWidthProperty().bind(buttons.widthProperty());
return layout;
}

private void handleaccltrs(VBox layout) {
layout.addEventFilter(KeyEvent.KEY_PRESSED, new EventHandler<KeyEvent>() {
@Override
public void handle(KeyEvent keyEvent) {
Button activated = accltrs.get(keyEvent.getText());
if (activated != null) {
activated.fire();
}
}
});
}

private TextField createScreen() {
final TextField screen = new TextField();
screen.setStyle("-fx-background-color: aquamarine;");
screen.setAlignment(Pos.CENTER_RIGHT);
screen.setEditable(false);
screen.textProperty().bind(Bindings.format("%.0f", value));
return screen;
}

private TilePane createButtons() {
TilePane buttons = new TilePane();
buttons.setVgap(7);
buttons.setHgap(7);
buttons.setPrefColumns(TMPLATE[0].length);
for (String[] r: TMPLATE) {
for (String s: r) {
buttons.getChildren().add(createButton(s));
}
}
return buttons;
}

private Button createButton(final String s) {
Button button = makeStandardButton(s);

if (s.matches("[0-9]")) {
makeNumericButton(s, button);
} else {
final ObjectProperty<Op> triggerOp = determineOperand(s);
if (triggerOp.get() != Op.NOOP) {
makeOperandButton(button, triggerOp);
} else if ("c".equals(s)) {
makeClearButton(button);
} else if ("=".equals(s)) {
makeEqualsButton(button);
}
}

return button;
}

private ObjectProperty<Op> determineOperand(String s) {
final ObjectProperty<Op> triggerOp = new SimpleObjectProperty<>(Op.NOOP);
switch (s) {
case "+": triggerOp.set(Op.ADD); break;
case "-": triggerOp.set(Op.SUBTRACT); break;
case "*": triggerOp.set(Op.MULTIPLY); break;
case "/": triggerOp.set(Op.DIVIDE); break;
}
return triggerOp;
}

private void makeOperandButton(Button button, final ObjectProperty<Op> triggerOp) {
button.setStyle("-fx-base: lightgray;");
button.setOnAction(new EventHandler<ActionEvent>() {
@Override
public void handle(ActionEvent actionEvent) {
curOp = triggerOp.get();
}
});
}

private Button makeStandardButton(String s) {
Button button = new Button(s);
button.setStyle("-fx-base: beige;");
accltrs.put(s, button);
button.setMaxSize(Double.MAX_VALUE, Double.MAX_VALUE);
return button;
}

private void makeNumericButton(final String s, Button button) {
button.setOnAction(new EventHandler<ActionEvent>() {
@Override
public void handle(ActionEvent actionEvent) {
if (curOp == Op.NOOP) {
value.set(value.get() * 10 + Integer.parseInt(s));
} else {
stackValue.set(value.get());
value.set(Integer.parseInt(s));
stackOp = curOp;
curOp = Op.NOOP;
}
}
});
}

private void makeClearButton(Button button) {
button.setStyle("-fx-base: mistyrose;");
button.setOnAction(new EventHandler<ActionEvent>() {
@Override
public void handle(ActionEvent actionEvent) {
value.set(0);
}
});
}

private void makeEqualsButton(Button button) {
button.setStyle("-fx-base: ghostwhite;");
button.setOnAction(new EventHandler<ActionEvent>() {
@Override
public void handle(ActionEvent actionEvent) {
switch (stackOp) {
case ADD: value.set(stackValue.get() + value.get()); break;
case SUBTRACT: value.set(stackValue.get() - value.get()); break;
case MULTIPLY: value.set(stackValue.get() * value.get()); break;
case DIVIDE: value.set(stackValue.get() / value.get()); break;
}
}
});
}

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