import java.awt.FlowLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;

public class Main {
    public static void main(String[] args) {
        // Create and set up the window.
        JFrame frame = new JFrame("Hello World");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        // Add contents to the window.
        frame.setLayout(new FlowLayout());
        frame.add(new JLabel("Hello, world!"));
        frame.add(new JButton("OK"));

        // Display the window.
        frame.pack();
        frame.setVisible(true);
    }
}

frame.setContentPane(new MyPanel());