JavaFX simple calculator

JavaFx Events and Event Handling: Exercise-6 with Solution

Write a JavaFX program to build a simple calculator with digit buttons (0-9) and basic arithmetic operator buttons (+, -, *, /). Implement action listeners for each button (digits and operators) to perform calculations.

Sample Solution:

JavaFx Code:

//Main.java
import javafx.application.Application;
import javafx.geometry.Insets;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.layout.GridPane;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

public class Main extends Application {

    private StringBuilder inputBuffer = new StringBuilder();
    private String currentOperator = "";
    private double result = 0;

    private Label display;

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

    @Override
    public void start(Stage primaryStage) {
        primaryStage.setTitle("Calculator");

        GridPane grid = new GridPane();
        grid.setPadding(new Insets(10, 10, 10, 10));
        grid.setHgap(5);
        grid.setVgap(5);

        display = new Label("0");
        display.setPrefSize(150, 30);

        Button[] digitButtons = new Button[10];
        for (int i = 0; i < 10; i++) {
            digitButtons[i] = new Button(Integer.toString(i));
            digitButtons[i].setPrefSize(50, 30);
            final int digit = i;
            digitButtons[i].setOnAction(event -> onDigitClick(digit));
        }

        Button addButton = createOperatorButton("+");
        Button subtractButton = createOperatorButton("-");
        Button multiplyButton = createOperatorButton("*");
        Button divideButton = createOperatorButton("/");
        Button equalsButton = new Button("=");
        equalsButton.setOnAction(event -> onEqualsClick());

        grid.add(display, 0, 0, 4, 1);

        grid.addRow(1, digitButtons[7], digitButtons[8], digitButtons[9], addButton);
        grid.addRow(2, digitButtons[4], digitButtons[5], digitButtons[6], subtractButton);
        grid.addRow(3, digitButtons[1], digitButtons[2], digitButtons[3], multiplyButton);
        grid.addRow(4, digitButtons[0], equalsButton, divideButton);

        Scene scene = new Scene(grid, 210, 250);
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    private Button createOperatorButton(String operator) {
        Button button = new Button(operator);
        button.setPrefSize(50, 30);
        button.setOnAction(event -> onOperatorClick(operator));
        return button;
    }

    private void onDigitClick(int digit) {
        inputBuffer.append(digit);
        updateDisplay();
    }

    private void onOperatorClick(String operator) {
        if (inputBuffer.length() > 0) {
            if (!currentOperator.isEmpty()) {
                onEqualsClick();
            }
            currentOperator = operator;
            result = Double.parseDouble(inputBuffer.toString());
            inputBuffer.setLength(0);
        }
    }

    private void onEqualsClick() {
        if (inputBuffer.length() > 0) {
            double operand = Double.parseDouble(inputBuffer.toString());
            switch (currentOperator) {
                case "+":
                    result += operand;
                    break;
                case "-":
                    result -= operand;
                    break;
                case "*":
                    result *= operand;
                    break;
                case "/":
                    if (operand != 0) {
                        result /= operand;
                    } else {
                        inputBuffer.setLength(0);
                        inputBuffer.append("Error");
                        updateDisplay();
                        return;
                    }
                    break;
            }
            inputBuffer.setLength(0);
            inputBuffer.append(result);
            currentOperator = "";
            updateDisplay();
        }
    }

    private void updateDisplay() {
        String displayText = inputBuffer.length() > 0 ? inputBuffer.toString() : Double.toString(result);
        displayText = displayText.length() > 10 ? displayText.substring(0, 10) : displayText;
        display.setText(displayText);
    }
}

The above code creates a basic calculator with digit buttons (0-9) and basic arithmetic operator buttons (+, -, *, /). It supports calculations when you click the equals button (=). The program displays the result on the screen, handles errors such as division by zero, and limits the displayed value to 10 characters.

Sample Output:

Flowchart:

Java Code Editor:

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