//package howto;

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

public class Main extends Applet
{
   private Stack _s = null;
   private Panel _p = null;

   private TextField _tf = null;
   private Choice _ch = null;

   public void init()
   {
      setLayout(new BorderLayout());

      _s = new Stack();

      add("Center", _s);

      _p = new Panel();

      _tf = new TextField(15);

      _p.add(_tf);

      _ch = new Choice();

      _p.add(_ch);

      add("South", _p);
   }

   public boolean action(Event e, Object o)
   {
      if (e.target == _tf || e.target == _ch)
      {
         String str = (String)o;

         try
         {
            invoke(str);
         }
         catch (Exception exp)
         {
            panic(exp.toString());
         }

         _s.display();

         return true;
      }

      return false;
   }

   private void panic(String str)
   {
      System.out.println(str);
   }

   private void invoke(String str) throws Exception
   {
      Double d = null;

      try
      {
         d = new Double(str);
      }
      catch (NumberFormatException nfexp)
      {
         ;
      }

      if (d == null)
      {
         _ch.addItem(str);

         Class c = Class.forName("howto.operators." + str);

         Object o = c.newInstance();

         Operator op = (Operator)o;

         op.operate(_s);
      }
      else
      {
         _s.push(d.doubleValue());
      }
   }

   public Dimension preferredSize()
   {
      return new Dimension(300, 200);
   }

   public static void main(String [] args)
   {
      Frame f = new Frame("Main");

      Main m = new Main();

      m.init();

      f.add("Center", m);

      f.pack();

      f.show();
   }
}