Imagen fondo (clase extends JPanel)

package pruebasconimagenes;

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

public class PnlFondo extends javax.swing.JPanel{

public PnlFondo(){
//initComponents();

this.setSize(100,100);
Icon imgBoton = new ImageIcon(getClass().getResource("/pruebasconimagenes/bombay.jpg"));

}

public void paintComponent(Graphics g){

Dimension tamaño= getSize();
ImageIcon imagenFondo= new ImageIcon(getClass().getResource("/pruebasconimagenes/bombay.jpg"));
g.drawImage(imagenFondo.getImage(),0,0,imagenFondo.getImage().getWidth(this),imagenFondo.getImage().getHeight(this),null);
setOpaque(false);

super.paintComponent(g);

}

}

package pruebasconimagenes;

import java.applet.*;
import java.awt.*;

public class FrmPrincipal extends javax.swing.JFrame {

public FrmPrincipal(){

PnlFondo pnlFondo= new PnlFondo();
this.add(pnlFondo, BorderLayout.CENTER);
this.pack();

}

}


package pruebasconimagenes;

public class claseprincipal {

public static void main(String[]args){

FrmPrincipal uno=new FrmPrincipal();
uno.setVisible(true);

}

}