Pane

import java.awt.BorderLayout;


public class MainWindow extends JFrame {

	private JPanel contentPane;

	/**
	 * Launch the application.
	 */
	public static void main(String[] args) {
		EventQueue.invokeLater(new Runnable() {
			public void run() {
				try {
					MainWindow frame = new MainWindow();
					frame.setVisible(true);
				} catch (Exception e) {
					e.printStackTrace();
				}
			}
		});
	}

	/**
	 * Create the frame.
	 */
	public MainWindow() {
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		setBounds(100, 100, 450, 300);
		contentPane = new JPanel();
		contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
		setContentPane(contentPane);
		contentPane.setLayout(new FlowLayout(FlowLayout.CENTER, 5, 5));

		JPanel panel = new JPanel();
		contentPane.add(panel);

		JButton btnNewButton_1 = new JButton("New button");
		panel.add(btnNewButton_1);

		JButton btnNewButton_2 = new JButton("New button");
		panel.add(btnNewButton_2);

		JButton btnNewButton = new JButton("New button");
		panel.add(btnNewButton);
	}

}