Diferença nos códigos (GUI)

public class AgendaGUI extends JFrame {
	JButton addButton;
	JButton findButton;
	JButton showButton;
	JButton exitButton;
	//JLabel label1;
	//JLabel label2;
	
	public AgendaGUI() {
		super(">>> AGENDA <<<");
		setLayout(new GridBagLayout());
		
		GridBagConstraints gbl = new GridBagConstraints();
		
		gbl.insets = new Insets(20,20,0,0);
		gbl.anchor = GridBagConstraints.NORTHWEST;
						
		addButton = new JButton("Add");
		add(addButton, gbl);
		
		findButton = new JButton("Find");
		gbl.gridy = 1;
		add(findButton, gbl);
		
		showButton = new JButton("Show");
		gbl.gridy = 2;
		add(showButton, gbl);
		
		setSize(300, 300);
		setVisible(true);
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
	
	}
	
	public static void main(String[] args) {
		AgendaGUI ag = new AgendaGUI();
	}
}

public GUI2() {
		super(">>> AGENDA <<<");
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		
		Container c = getContentPane();
		c.setLayout(new GridBagLayout());
		
		GridBagConstraints gbl = new GridBagConstraints();
		
		gbl.insets = new Insets(20,20,0,0);
		gbl.anchor = GridBagConstraints.NORTHWEST; //essa linha aparentemente não serve p/ nada, quando deveria ajustar os componentes na tela
						
		addButton = new JButton("Add");
		c.add(addButton, gbl);
		
		findButton = new JButton("Find");
		gbl.gridy = 1;
		c.add(findButton, gbl);
		
		showButton = new JButton("Show");
		gbl.gridy = 2;
		c.add(showButton, gbl);
		
		setSize(300, 300);
		setVisible(true);
		
	
	}
	
	public static void main(String[] args) {
		GUI2 ag = new GUI2();
	}
}