Calculator.java

package JUnittasks;

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

public class Calculator extends JFrame {
    private final JTextField jTextField;
    private final JButton zero, one, two, three, four, five, six, seven, eight, nine;
    private final JButton add, sub, mul, div, dot, equal;
    private ButtonGroup buttonGroup;


    public Calculator () {
        super("Calculator");
        setLayout(new FlowLayout());

        jTextField = new JTextField(15);
        add(jTextField);

        seven = new JButton("7");
        add(seven);
        eight = new JButton("8");
        add(eight);
        nine = new JButton("9");
        add(nine);
        div = new JButton("/");
        add(div);
        four = new JButton("4");
        add(four);
        five = new JButton("5");
        add(five);
        six = new JButton("6");
        add(six);
        mul = new JButton("*");
        add(mul);
        one = new JButton("1");
        add(one);
        two = new JButton("2");
        add(two);
        three = new JButton("3");
        add(three);
        sub = new JButton("-");
        add(sub);
        zero = new JButton("0");
        add(zero);
        dot = new JButton(".");
        add(dot);
        equal = new JButton("=");
        add(equal);
        add = new JButton("+");
        add(add);

        buttonGroup = new ButtonGroup();
        buttonGroup.add(seven);
        buttonGroup.add(eight);
        buttonGroup.add(nine);
        buttonGroup.add(div);
        buttonGroup.add(four);
        buttonGroup.add(five);
        buttonGroup.add(six);
        buttonGroup.add(mul);
        buttonGroup.add(one);
        buttonGroup.add(two);
        buttonGroup.add(three);
        buttonGroup.add(sub);
        buttonGroup.add(zero);
        buttonGroup.add(dot);
        buttonGroup.add(equal);
        buttonGroup.add(add);
    }

    public static void main(String[] args) {
        Calculator calculator = new Calculator();
        calculator.setSize(200, 200);
        calculator.setResizable(false);
        calculator.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        calculator.setVisible(true);
        calculator.setLocationRelativeTo(null);
    }
}