SimpleCalculator/SimpleCalculator.java

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

public class SimpleCalculator extends JFrame {

    private JTextField display;
    private JPanel panel;
    private double operand1 = 0;
    private double operand2 = 0;
    private char operator;
    private boolean userIsTypingSecondNumber = false;

    public SimpleCalculator() {
        setTitle("Simple Calculator");
        setSize(400, 500);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLocationRelativeTo(null);

        // Display text field
        display = new JTextField();
        display.setEditable(false);
        display.setHorizontalAlignment(SwingConstants.RIGHT);
        add(display, BorderLayout.NORTH);

        // Panel for buttons
        panel = new JPanel();
        panel.setLayout(new GridLayout(5, 4, 10, 10));

        // Add numbers and operations to panel
        String[] buttons = {
                "7", "8", "9", "/",
                "4", "5", "6", "*",
                "1", "2", "3", "-",
                "0", ".", "=", "+",
                "C"
        };

        for (String text : buttons) {
            JButton button = new JButton(text);
            button.setFont(new Font("Verdana", Font.PLAIN, 24));
            button.setFocusable(false);
            panel.add(button);
            button.addActionListener(new ButtonClickListener());
        }

        add(panel, BorderLayout.CENTER);
    }

    private class ButtonClickListener implements ActionListener {
        @Override
        public void actionPerformed(ActionEvent e) {
            String command = e.getActionCommand();

            if ("0123456789.".contains(command)) {
                display.setText(display.getText().concat(command));
            } else if ("+-*/".contains(command)) {
                operand1 = Double.parseDouble(display.getText());
                operator = command.charAt(0);
                userIsTypingSecondNumber = true;
                display.setText(""); // Clear the display for the next number
            } else if (command.equals("=")) {
                if (userIsTypingSecondNumber) {
                    operand2 = Double.parseDouble(display.getText());
                    double result = 0;
                    switch (operator) {
                        case '+':
                            result = operand1 + operand2;
                            break;
                        case '-':
                            result = operand1 - operand2;
                            break;
                        case '*':
                            result = operand1 * operand2;
                            break;
                        case '/':
                            if (operand2 != 0) {
                                result = operand1 / operand2;
                            } else {
                                display.setText("Error");
                                return;
                            }
                            break;
                    }
                    display.setText(String.valueOf(result));
                    operand1 = result; // Store the result for possible chain operations
                    userIsTypingSecondNumber = false; // Reset for next operation
                }
            } else if (command.equals("C")) {
                display.setText("");
                operand1 = 0;
                operand2 = 0;
                userIsTypingSecondNumber = false;
            }
        }
    }

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