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

public class SumTextFields extends JFrame 
    implements ActionListener {

    private JTextField number1Field, number2Field, sumField;
    private JLabel equalsLabel;
    private JButton plusButton;

    public static void main(String[] args) {
        SumTextFields frame = new SumTextFields();
        frame.setSize(350, 100);
        frame.createGUI();
        frame.show();
    }

    private void createGUI() {
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        Container window = getContentPane();
        window.setLayout(new FlowLayout());

        number1Field = new JTextField(7);
        window.add(number1Field);

        plusButton = new JButton("+");
        window.add(plusButton);
        plusButton.addActionListener(this);

        number2Field = new JTextField(7);
        window.add(number2Field);

        equalsLabel = new JLabel("  =  ");
        window.add(equalsLabel);

        sumField = new JTextField(7);
        window.add(sumField);
    }

    public void actionPerformed(ActionEvent event) {
        int number1 = Integer.parseInt(number1Field.getText());
        int number2 = Integer.parseInt(number2Field.getText());
        sumField.setText(Integer.toString(number1 + number2));
    }
}