Calculator.java

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

public class Calculator extends JFrame implements ActionListener {
    private JTextField display;
    private double firstOperand = Double.NaN;
    private String currentOp = "";
    private boolean startNewNumber = true;

    public Calculator() {
        setTitle("Scientific Calculator");
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setLocationRelativeTo(null);

        // Comfortable larger size; we'll pack after setting preferred sizes
        getContentPane().setBackground(new Color(240, 240, 245));
        setLayout(new BorderLayout(12,12));

        display = new JTextField();
        display.setFont(new Font("SansSerif", Font.BOLD, 48));
        display.setHorizontalAlignment(JTextField.RIGHT);
        display.setEditable(false);
        display.setText("0");
        display.setBackground(new Color(28, 30, 34));
        display.setForeground(Color.WHITE);
        display.setBorder(BorderFactory.createCompoundBorder(
            BorderFactory.createEmptyBorder(12, 12, 12, 12),
            BorderFactory.createLineBorder(new Color(50, 50, 60), 2)));

        // place display in a top panel to control padding/height
        JPanel topPanel = new JPanel(new BorderLayout());
        topPanel.setBackground(getContentPane().getBackground());
        display.setPreferredSize(new Dimension(760, 140));
        topPanel.setBorder(BorderFactory.createEmptyBorder(14, 14, 10, 14));
        topPanel.add(display, BorderLayout.CENTER);
        add(topPanel, BorderLayout.NORTH);

        JPanel panel = new JPanel();
        panel.setBackground(getContentPane().getBackground());
        panel.setLayout(new GridLayout(6, 4, 10, 10));

        String[] buttons = {
            "AC", "pi", "x^2", "sqrt",
            "7", "8", "9", "/",
            "4", "5", "6", "*",
            "1", "2", "3", "-",
            "0", ".", "=", "+",
            "sin", "cos", "tan", "log"
        };

        for (String text : buttons) {
            JButton b = new JButton(text);
            b.setFont(new Font("SansSerif", Font.BOLD, 20));
            b.setFocusPainted(false);
            b.addActionListener(this);
            b.setPreferredSize(new Dimension(140, 72));

            // Color coding
            if (text.equals("AC")) {
                b.setBackground(new Color(220, 80, 80));
                b.setForeground(Color.WHITE);
            } else if (text.equals("=") ) {
                b.setBackground(new Color(80, 180, 120));
                b.setForeground(Color.WHITE);
            } else if (text.matches("[0-9]|") || text.equals(".")) {
                b.setBackground(Color.WHITE);
                b.setForeground(Color.DARK_GRAY);
            } else if (text.equals("+") || text.equals("-") || text.equals("*") || text.equals("/")) {
                b.setBackground(new Color(255, 165, 60));
                b.setForeground(Color.WHITE);
            } else {
                // scientific/function buttons
                b.setBackground(new Color(80, 140, 220));
                b.setForeground(Color.WHITE);
            }

            b.setBorder(BorderFactory.createLineBorder(new Color(200,200,200)));
            panel.add(b);
        }

        add(panel, BorderLayout.CENTER);

        // Final sizing
        pack();
        setSize(820, 720);
        setResizable(false);
    }

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

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

        try {
            if (cmd.equals("AC")) {
                clearAll();
                return;
            }

            if (isNumberOrDot(cmd)) {
                if (startNewNumber) {
                    display.setText(cmd.equals(".") ? "0." : cmd);
                    startNewNumber = false;
                } else {
                    if (cmd.equals(".") && display.getText().contains(".")) return;
                    display.setText(display.getText().equals("0") && !cmd.equals(".") ? cmd : display.getText() + cmd);
                }
                return;
            }

            if (isOperator(cmd)) {
                applyPendingOperator();
                currentOp = cmd;
                startNewNumber = true;
                return;
            }

            if (cmd.equals("=")) {
                applyPendingOperator();
                currentOp = "";
                startNewNumber = true;
                return;
            }

            // Scientific functions apply immediately to current display value
            if (isScientific(cmd)) {
                double val = parseDisplay();
                double result = 0;
                switch (cmd) {
                    case "sin": result = Math.sin(Math.toRadians(val)); break;
                    case "cos": result = Math.cos(Math.toRadians(val)); break;
                    case "tan": result = Math.tan(Math.toRadians(val)); break;
                    case "log": result = Math.log10(val); break;
                    case "sqrt": result = Math.sqrt(val); break;
                    case "x^2": result = val * val; break;
                    case "pi": result = Math.PI; break;
                    default: throw new UnsupportedOperationException("Unknown function: " + cmd);
                }
                display.setText(formatResult(result));
                startNewNumber = true;
                return;
            }

        } catch (ArithmeticException ex) {
            showError("Error: Division by zero is not allowed");
            clearAll();
        } catch (NumberFormatException ex) {
            showError("Invalid Input");
            clearAll();
        } catch (Exception ex) {
            showError("An unexpected error occurred: " + ex.getMessage());
            clearAll();
        }
    }

    private boolean isNumberOrDot(String s) {
        return s.matches("\\d") || s.equals(".");
    }

    private boolean isOperator(String s) {
        return s.equals("+") || s.equals("-") || s.equals("*") || s.equals("/");
    }

    private boolean isScientific(String s) {
        return s.equals("sin") || s.equals("cos") || s.equals("tan") || s.equals("log") || s.equals("sqrt") || s.equals("x^2") || s.equals("pi");
    }

    private void applyPendingOperator() {
        double displayed = parseDisplay();
        if (Double.isNaN(firstOperand)) {
            firstOperand = displayed;
            display.setText(formatResult(firstOperand));
        } else if (!currentOp.isEmpty()) {
            double result = 0;
            switch (currentOp) {
                case "+": result = firstOperand + displayed; break;
                case "-": result = firstOperand - displayed; break;
                case "*": result = firstOperand * displayed; break;
                case "/":
                    if (displayed == 0) throw new ArithmeticException("Division by zero");
                    result = firstOperand / displayed; break;
                default: throw new UnsupportedOperationException("Unknown operator: " + currentOp);
            }
            firstOperand = result;
            display.setText(formatResult(result));
        }
    }

    private double parseDisplay() {
        String txt = display.getText();
        if (txt == null || txt.trim().isEmpty()) throw new NumberFormatException("Empty input");
        return Double.parseDouble(txt);
    }

    private String formatResult(double v) {
        if (Double.isInfinite(v) || Double.isNaN(v)) return "Error";
        if (Math.rint(v) == v) return String.valueOf((long)v);
        return String.valueOf(v);
    }

    private void clearAll() {
        display.setText("0");
        firstOperand = Double.NaN;
        currentOp = "";
        startNewNumber = true;
    }

    private void showError(String msg) {
        JOptionPane.showMessageDialog(this, msg, "Error", JOptionPane.ERROR_MESSAGE);
    }
}