SimpleCalculator.java

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class SimpleCalculator extends JFrame implements ActionListener {
    private JTextField display;
    private double firstNumber = 0;
    private String operator = "";
    private boolean startNewNumber = true;

    public SimpleCalculator() {
        setTitle("Simple Calculator");
        setSize(400, 400);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); // Corrected 'setDefaultCloseOperator'
        setLayout(new BorderLayout());

        // Display field setup
        display = new JTextField();
        display.setEditable(false);
        display.setFont(new Font("Arial", Font.BOLD, 24)); // Fixed missing double quotes around "Arial"
        add(display, BorderLayout.NORTH);

        // Button panel setup
        JPanel buttonPanel = new JPanel();
        buttonPanel.setLayout(new GridLayout(4, 4));

        // Button labels
        String[] buttons = {
            "7", "8", "9", "/",
            "4", "5", "6", "*",
            "1", "2", "3", "-",
            "0", "C", "=", "+"
        };

        // Add buttons to the panel
        for (String text : buttons) {
            JButton button = new JButton(text);
            button.setFont(new Font("Arial", Font.BOLD, 20)); // Fixed typo 'Fon' to 'Font'
            button.addActionListener(this);
            buttonPanel.add(button);
        }

        add(buttonPanel, BorderLayout.CENTER);
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        String command = e.getActionCommand();

        // Handle number inputs
        if ("0123456789".contains(command)) {
            if (startNewNumber) {
                display.setText(command);
                startNewNumber = false;
            } else {
                display.setText(display.getText() + command);
            }
        }
        // Handle operator inputs
        else if ("/*-+".contains(command)) {
            firstNumber = Double.parseDouble(display.getText());
            operator = command;
            startNewNumber = true;
        }
        // Handle equals input
        else if (command.equals("=")) {
            try {
                double secondNumber = Double.parseDouble(display.getText());
                double result = 0;

                switch (operator) {
                    case "/":
                        if (secondNumber == 0) {
                            throw new ArithmeticException("Cannot divide by zero");
                        }
                        result = firstNumber / secondNumber;
                        break;
                    case "*":
                        result = firstNumber * secondNumber;
                        break;
                    case "-":
                        result = firstNumber - secondNumber;
                        break;
                    case "+":
                        result = firstNumber + secondNumber;
                        break;
                }

                display.setText(String.valueOf(result));
                startNewNumber = true;
            } catch (ArithmeticException ex) {
                display.setText("Error: " + ex.getMessage());
                startNewNumber = true;
            } catch (NumberFormatException ex) {
                display.setText("Error: Invalid Number");
            }
        }
        // Handle clear input
        else if (command.equals("C")) {
            display.setText("");
            startNewNumber = true;
        }
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            SimpleCalculator frame = new SimpleCalculator();
            frame.setVisible(true);
        });
    }
}