Ayuda principiante Java

package marcodeprueba;
import javax.swing.*;
import java.awt.*;
public class Marco extends JFrame{
private JPanel panelPrincipal;
private JButton boton=new JButton();
private JButton boton2=new JButton();

public Marco() {
jbInit();
}
private void jbInit(){
this.setSize(400,300);
this.setTitle("Ejemplo con botón");

panelPrincipal=(JPanel)this.getContentPane();
panelPrincipal.setBackground(Color.red);
panelPrincipal.setLayout(null);

boton.setBounds(120,180,100,70);
boton.setText("Aceptar");
boton.setForeground(Color.blue);

panelPrincipal.add(boton);

boton2.setBounds(120,180,100,70);
boton2.setText("Cancelar");
boton2.setForeground(Color.blue);

panelPrincipal.add(boton2);

}
}