[JAVA]risanje - BufferedImage

a mi kdo pove, zakaj to ne deluje? Nej bi narisalo crn pravokotnik ne naredi pa nic.

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

public class risanje extends JFrame{

panela panel;
JPanel vsebina;

risanje(){

vsebina = new JPanel();
setSize(500, 500);
setTitle("krneki");
setBackground(Color.white);
panel = new panela();
vsebina.add(panel);
}

}

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

public class panela extends JPanel{

static BufferedImage slika;
static Graphics g;
public void paintComponent(){
super.paintComponent(g);
// if(slika==null){
slika = new BufferedImage(50, 50, BufferedImage.TYPE_INT_RGB);
g=slika.getGraphics();
Graphics g2 = (Graphics2D)g;

g2.setColor(Color.black);
g2.drawRect(10, 10, 20, 30);
g2.drawImage(slika, 0, 0, null);

//}
}
}

import java.awt.*;

public class glavno{

public static void main(String []Args){

risanje okno = new risanje();
okno.show();
}
}

Upam da mi boste lahko pomagali ker tole me ze prav resno zivcira