נושא: בעיה עם J2ME

import javax.microedition.lcdui.*;
import javax.microedition.midlet.*;

public class GhostDog
    extends MIDlet
    implements CommandListener {
  private Form mMainForm;
  private TextField tfA;
  private TextField tfB;
  private TextField tfC;
  Command cmdCalc;
  Command cmdExit;
  Form m2;
 
  public GhostDog() {
    mMainForm = new Form("x^2 Calc");
    mMainForm.append(new StringItem(null, "Insert a, b and c"));
    tfA=new TextField("a:","",5,TextField.ANY);
    tfB=new TextField("b:","",5,TextField.ANY);
    tfC=new TextField("c:","",5,TextField.ANY);
    cmdCalc=new Command("Calc!", Command.ITEM,0);
    cmdExit=new Command("Exit", Command.SCREEN,1);
    mMainForm.append(tfA);
    mMainForm.append(tfB);
    mMainForm.append(tfC);
    mMainForm.addCommand(cmdCalc);
    mMainForm.addCommand(cmdExit);
    mMainForm.setCommandListener(this);
  }
 
  public void startApp() {
    Display.getDisplay(this).setCurrent(mMainForm);
  }
 
  public void pauseApp() {}
 
  public void destroyApp(boolean unconditional) {}

  public double Abso(double x)
  {
   if (x<0) { return 0-x; }
   else return x;
  }
  public double Sqrt(double x)
  {
   double c = x;
      double t = c;
      double EPSILON = 1E-15;    // relative error tolerance

      while (Abso(t - c/t) > t*EPSILON) {
         t = (c/t + t) / 2.0;
      } 
      return t;
  }
  public void commandAction(Command cm, Displayable s) {
    if (cm==cmdCalc)
    {
     double a=Double.parseDouble(tfA.getString());
     double b=Double.parseDouble(tfB.getString());
     double c=Double.parseDouble(tfC.getString());
       double x1,x2;
       String sx1=new String();
       String sx2=new String();
       String done=new String();
       if (((b*b)-(4*a*c))>0)
       {
        x1=(-b+Sqrt((b*b-(4*a*c))))/(2*a);
        x2=(-b-Sqrt((b*b-(4*a*c))))/(2*a);
        sx1="" + x1;
        sx2="" + x2;
        done="X1="+sx1+" X2="+sx2;
       }
       else if (((b*b)-(4*a*c))==0)
       {
        x1=-b/(2*a);
        sx1="" +x1;
        done="X="+sx1;
       }
       else done="Unsolvable.";
       
       m2=new Form("Answer:");
       m2.append(new StringItem(null, done));
       Display.getDisplay(this).setCurrent(m2);
     
    }
    else if (cm==cmdExit)
    {
     destroyApp(false);
     notifyDestroyed();
    }
  }
}