Calculatrice java

Bonjour,

voici mon programme d'une calculette java, j'aimerai juste k vs me completez pour faire l'addition
import java.awt.*;


public class Calculatrice extends Frame
{
char operateur;
TextField display = new TextField(20);
Button[] chiffres = new Button [10];
Button[] operat = new Button [8];
Canvas vide = new Canvas();
String t = "";
Panel[] rangee = new Panel[6];
String bouton_clic="";

Calculatrice ()
{
for (int i=0;i<=9;i++)
{
chiffres [i] = new Button (""+i);
}
operat[0] = new Button("c");
operat[1] = new Button("/");
operat[2] = new Button("*");
operat[3] = new Button("-");
operat[4] = new Button("+/-");
operat[5] = new Button(".");
operat[6] = new Button("+");
operat[7] = new Button("=");

for (int i=0;i<=5;i++)
{
rangee[i] = new Panel();
}

GridLayout grille = new GridLayout (6,0,5,5);
setLayout(grille);

for (int j=0;j<=5;j++)
{
GridLayout ligne = new GridLayout(1,4,5,5);
rangee[j].setLayout(ligne);
}
display.setBackground(Color.white);
rangee[0].add(display);
add(rangee[0]);
int min=7, max=9, k;
for (k=1; k<=3;k++)
{
for (int j=min; j<=max;j++)
rangee[k].add(chiffres[j]);
rangee[k].add(operat[k]);
add (rangee[k]);
min=min-3; max=max-3;
}
rangee[4].add(chiffres[0]);
rangee[4].add(operat[4]);
rangee[4].add(operat[5]);
rangee[4].add(operat[6]);
add(rangee[4]);
rangee[5].add(operat[0]);
rangee[5].add(vide);
rangee[5].add(vide);
rangee[5].add(operat[7]);
add(rangee[5]);

}

public boolean action (Event e, Object Ob)
{
bouton_clic=String.valueOf(Ob);
if (bouton_clic.equals("c"))
effacer();
else
{ repaint(); }
return true;
}
public void paint(Graphics g)
{
t=display.getText();
t+=bouton_clic;
display.setText(t);
}
public void effacer()
{ display.setText("");
}

public static void main(String[] args)
{
Calculatrice maCalcul = new Calculatrice();
maCalcul.setSize(200, 300);
maCalcul.setVisible(true);
}

}