CalculatorApp.java

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

public class CalculatorApp {
    private JFrame frame;
    private JTextField textField;

    private double num1 = 0, num2 = 0;
    private String operator = "";

    public CalculatorApp() {
        frame = new JFrame("Calculator");
        frame.setLayout(new BorderLayout());

        textField = new JTextField();
        textField.setEditable(false);
        frame.add(textField, BorderLayout.NORTH);

        JPanel panel = new JPanel(new GridLayout(4, 4));
        frame.add(panel, BorderLayout.CENTER);

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

        for (String button : buttons) {
            JButton btn = new JButton(button);
            btn.addActionListener(new ButtonClickListener());
            panel.add(btn);
        }

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(300, 300);
        frame.setVisible(true);
    }

    private class ButtonClickListener implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            String command = e.getActionCommand();
            if (Character.isDigit(command.charAt(0)) || command.equals(".")) {
                textField.setText(textField.getText() + command);
            } else if (command.equals("C")) {
                textField.setText("");
            } else if (command.equals("=")) {
                num2 = Double.parseDouble(textField.getText());
                double result = 0;
                switch (operator) {
                    case "+":
                        result = num1 + num2;
                        break;
                    case "-":
                        result = num1 - num2;
                        break;
                    case "*":
                        result = num1 * num2;
                        break;
                    case "/":
                        result = num1 / num2;
                        break;
                }
                textField.setText(String.valueOf(result));
                num1 = result;
            } else {
                operator = command;
                num1 = Double.parseDouble(textField.getText());
                textField.setText("");
            }
        }
    }

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