How to Create a Basic Calculator in Swing?

The following program demonstrates How to Create a Basic Calculator in Swing.

Creating a simple Swing calculator with basic arithmetic functions (addition, subtraction, multiplication, division) involves creating a graphical user interface (GUI) with buttons for numbers, operators, and a text field to display the input and result. The following code shows an example of a basic Swing calculator.

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

public class CalculatorApp extends JFrame {
    private JTextField textField;
    private JButton[] numberButtons = new JButton[10];
    private JButton addButton, subButton, mulButton, divButton, eqButton, clrButton;
    private double num1, num2, result;
    private char operator;

    public CalculatorApp() {
        setTitle("Calculator");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(300, 400);
        setLayout(new BorderLayout());

        textField = new JTextField();
        textField.setFont(new Font("Arial", Font.PLAIN, 24));
        textField.setHorizontalAlignment(JTextField.RIGHT);
        textField.setEditable(false);
        add(textField, BorderLayout.NORTH);

        JPanel buttonPanel = new JPanel();
        buttonPanel.setLayout(new GridLayout(4, 4, 10, 10));

        for (int i = 0; i < 10; i++) {
            numberButtons[i] = new JButton(String.valueOf(i));
            numberButtons[i].setFont(new Font("Arial", Font.PLAIN, 20));
            numberButtons[i].addActionListener(new NumberButtonListener());
            buttonPanel.add(numberButtons[i]);
        }

        addButton = new JButton("+");
        subButton = new JButton("-");
        mulButton = new JButton("*");
        divButton = new JButton("/");
        eqButton = new JButton("=");
        clrButton = new JButton("C");

        addButton.addActionListener(new OperatorButtonListener('+'));
        subButton.addActionListener(new OperatorButtonListener('-'));
        mulButton.addActionListener(new OperatorButtonListener('*'));
        divButton.addActionListener(new OperatorButtonListener('/'));
        eqButton.addActionListener(new EqualsButtonListener());
        clrButton.addActionListener(new ClearButtonListener());

        buttonPanel.add(addButton);
        buttonPanel.add(subButton);
        buttonPanel.add(mulButton);
        buttonPanel.add(divButton);
        buttonPanel.add(eqButton);
        buttonPanel.add(clrButton);

        add(buttonPanel, BorderLayout.CENTER);

        setVisible(true);
    }

    class NumberButtonListener implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            String currentText = textField.getText();
            JButton buttonClicked = (JButton) e.getSource();
            String buttonText = buttonClicked.getText();
            textField.setText(currentText + buttonText);
        }
    }

    class OperatorButtonListener implements ActionListener {
        private char operator;

        public OperatorButtonListener(char operator) {
            this.operator = operator;
        }

        public void actionPerformed(ActionEvent e) {
            String currentText = textField.getText();
            num1 = Double.parseDouble(currentText);
            CalculatorApp.this.operator = operator;
            textField.setText("");
        }
    }

    class EqualsButtonListener implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            String currentText = textField.getText();
            num2 = Double.parseDouble(currentText);

            switch (operator) {
                case '+':
                    result = num1 + num2;
                    break;
                case '-':
                    result = num1 - num2;
                    break;
                case '*':
                    result = num1 * num2;
                    break;
                case '/':
                    if (num2 != 0) {
                        result = num1 / num2;
                    } else {
                        textField.setText("Error");
                        return;
                    }
                    break;
            }

            textField.setText(String.valueOf(result));
        }
    }

    class ClearButtonListener implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            textField.setText("");
            num1 = num2 = result = 0;
            operator = '\0';
        }
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                new CalculatorApp();
            }
        });
    }
}

This program creates a basic calculator GUI with buttons for digits, arithmetic operators (+, -, *, /), an equals (=) button for calculation, and a clear (C) button to reset the input. It uses event listeners to handle user interactions and perform arithmetic operations.

Further Reading