SwingArithmetics.java

// school work
import java.awt.*; //using awt's layouts
import java.awt.event.*; //using awt's event classes and listener interfaces
import javax.swing.*; //using swing's components and container

//a swing application extends from javax.swing.JFrame

public class SwingArithmetics extends JFrame {
    private JTextField tfNumber1, tfNumber2, tfResult;
    private JButton btnAdd, btnSub, btnMulti, btnDiv, btnRemain, btnClear;
    private double number1, number2, result;

    //constructor to set up ui components and event handlers

    public SwingArithmetics() {
        //swing components should be added to the content-pane of the JFrame
        Container cp = getContentPane();
        //set this container to grid layout of 6 rows and 2 columns
        cp.setLayout(new GridLayout(6, 2, 10, 3));

        //components are added left-to-right, top-to-bottom
        cp.add(new JLabel("First Number "));
        tfNumber1 = new JTextField(10);
        tfNumber1.setHorizontalAlignment(JTextField.RIGHT);
        cp.add(tfNumber1);

        cp.add(new JLabel("Second Number "));
        tfNumber2 = new JTextField(10);
        tfNumber2.setHorizontalAlignment(JTextField.RIGHT);
        cp.add(tfNumber2);

        cp.add(new JLabel("Result "));
        tfResult = new JTextField(10);
        tfResult.setHorizontalAlignment(JTextField.RIGHT);
        cp.add(tfResult);

        btnAdd = new JButton("+");
        cp.add(btnAdd);
        btnAdd.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent evt) {
                number1 = Integer.parseInt(tfNumber1.getText());
                number2 = Integer.parseInt(tfNumber2.getText());

                result = number1 + number2; //to calculate the sum

                tfResult.setText(result + "");
            }
        });

        btnSub = new JButton("-");
        cp.add(btnSub);
        btnSub.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent evt) {
                number1 = Integer.parseInt(tfNumber1.getText());
                number2 = Integer.parseInt(tfNumber2.getText());

                result = number1 - number2;

                tfResult.setText(result + "");
            }
        });

        btnMulti = new JButton("*");
        cp.add(btnMulti);
        btnMulti.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent evt) {
                number1 = Integer.parseInt(tfNumber1.getText());
                number2 = Integer.parseInt(tfNumber2.getText());

                result = number1 * number2;

                tfResult.setText(result + "");
            }
        });

        btnDiv = new JButton("/");
        cp.add(btnDiv);
        btnDiv.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent evt) {
                number1 = Integer.parseInt(tfNumber1.getText());
                number2 = Integer.parseInt(tfNumber2.getText());

                result = number1 / number2;

                tfResult.setText(result + "");
            }
        });

        btnRemain = new JButton("%");
        cp.add(btnRemain);
        btnRemain.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent evt) {
                number1 = Integer.parseInt(tfNumber1.getText());
                number2 = Integer.parseInt(tfNumber2.getText());

                result = number1 % number2;

                tfResult.setText(result + "");
            }
        });

        btnClear = new JButton("CLEAR");
        cp.add(btnClear);
        btnClear.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent evt) {

                tfNumber1.setText(""); //to clear num 1 field
                tfNumber2.setText(""); //to clear num 2 field
                tfResult.setText(""); //to clear result field
            }
        });

        setDefaultCloseOperation(EXIT_ON_CLOSE); // for the "window-close" button
        setTitle("Swing Arithmetics");
        setSize(300, 170);
        setVisible(true);
    }

    // The entry main() method
    public static void main(String[] args) {
        // For thread safety, use the event-dispatching thread to construct UI
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new SwingArithmetics(); // Let the constructor does the job
            }
        });
    }
}