item stat change

package hello;
import java.lang.*;
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
public class Midlet extends MIDlet
implements CommandListener, ItemStateListener {
Display display;
Form frm;
TextField num1, num2, res;
String ops[];
ChoiceGroup cg;
Command exitCmd;
public Midlet () {
frm = new Form ("SimpleCalculator");
exitCmd = new Command("Exit",Command.EXIT,0);
frm.addCommand(exitCmd);
frm.setCommandListener(this);
ops = new String[]{"add", "subtract", "multiply", "divide"};
cg = new ChoiceGroup("Command", ChoiceGroup.EXCLUSIVE, ops, null);
frm.setItemStateListener(this);
num1 = new TextField("Number A","",10,TextField.DECIMAL);
num2 = new TextField("Number B","",10,TextField.DECIMAL);
res = new TextField("Result =","",16,TextField.UNEDITABLE);
frm.append(num1); frm.append(num2);
frm.append(cg);
frm.append(res);
}
public void startApp() {
if(display==null) {
display = Display.getDisplay (this);
//6 MORE ITEMS FOR FORMS 18
}
display.setCurrent (frm);
}
public void itemStateChanged(Item x) {
if(x!=cg) return;
int opInd=cg.getSelectedIndex();
double r;
double n1=Double.parseDouble(num1.getString());
double n2=Double.parseDouble(num2.getString());
if(opInd==0) { // add
r = n1 + n2;
} else if(opInd==1) { // subtract
r = n1 - n2;
} else if(opInd==2) { // multiply
r = n1 * n2;
} else if(opInd==3) { // divide
r = n1 / n2;
} else {
r = 0;
}
String rs = Double.toString(r);
if(rs.length()<=16) res.setString(rs);
else res.setString(rs.substring(0,16));
}
public void commandAction(Command c, Displayable s) {
if(c==exitCmd) {
destroyApp(false);
notifyDestroyed();
} else { } // shouldnt happen
}
public void pauseApp() { }
public void destroyApp(boolean unconditional) { }
}