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

class LeftRightButton extends JPanel
                      implements ActionListener {
    private int x = 20;
    private JButton lBtn, rBtn;
    public LeftRightButton() {
        setPreferredSize(new Dimension(200, 70));
        lBtn = new JButton("Left");  rBtn = new JButton("Right");
        lBtn.addActionListener(this);     rBtn.addActionListener(this);
        setLayout(new FlowLayout());      add(lBtn); add(rBtn);
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.drawString("HELLO WORLD!", x, 55);
    }

    public void actionPerformed(ActionEvent e) {
        Object source = e.getSource();
        if (source == lBtn) x -= 10; else if (source == rBtn) x += 10;
        repaint();
    }
}
void main() {
    SwingUtilities.invokeLater(() -> {
        JFrame frame = new JFrame("ボタン");
        frame.add(new LeftRightButton());
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    });
}