import java.awt.*;
import java.awt.event.*;
import java.text.*;
// import java.util.*;
// Internationalized numeric data entry.  This revision 
// traps keyPressed() in hopes MSIE will accommodate it.
// Comments: mailto:adahlman@jps.net
//
// While I wrote this myself, the debug process dragged on and 
//  on until I looked at a similar class courtesy of Peter Jakab 
//  and John Akerley.  Their code copyright IBM & licensed with
//  Nilsson & Jakab's book, Designing JavaBeans using VAJ2.
public class NumericTextField extends TextField implements KeyListener{
   protected static final String numbers = "0123456789";
   protected static  String firstDigit;
   static char dsep;
   static char gsep;
   static int gsize;

   public NumericTextField() {
      this( "", 0 );
   }

   public NumericTextField( int columns ) {
      this( "", columns );
   }

   public NumericTextField( String text ) {
      this( text, text.length() );
   }

   public NumericTextField( String text, int columns ) {
      super( text, columns );
      addKeyListener(this);

      // Internationalize the text field so that it requires a localized
      //  decimal separator (often a comma), but insist that '-' or '+' be
      //  the first digit, regardless of locale.
      DecimalFormat df = ( (DecimalFormat)NumberFormat.getNumberInstance() );
      DecimalFormatSymbols dfs = df.getDecimalFormatSymbols();
      dsep = dfs.getDecimalSeparator();
      char minus = dfs.getMinusSign();
      char plus = '+';
      firstDigit = String.valueOf(minus) + String.valueOf(plus) + numbers;

      // Some code to show how the text field is influenced by the default locale...
//      Locale loc = Locale.getDefault();
//      System.out.println("Language and country are: " + loc.getDisplayLanguage() 
//                                              + " - " + loc.getDisplayCountry() );
//      System.out.println("First digit may also be: '" + plus + "' or '" + minus 
//                        +"'.  The decimal separator is: '" + dsep + "'");
   }

   // implement KeyListener interface (overriding the methods
   //  inherited from Component.  Those keys we want to pass
   //  along, to the component or to an ancestor, are not consume()d.
   public void keyTyped(   KeyEvent ev ) {  }
   public void keyReleased(KeyEvent ev ) {  }
   public void keyPressed( KeyEvent ev ) {  
      if( ev.isActionKey() )
         return;

      int ch = (int)ev.getKeyChar();

      // pass legal numbers and signs
      if( getCaretPosition() == 0 ) {
         if( firstDigit.indexOf(ch) > -1 )
            return;
      } else
      if( numbers.indexOf(ch) > -1 ) {
      
         return;
      }
      // pass editing keys
      if( ch == KeyEvent.VK_BACK_SPACE
               || ch == KeyEvent.VK_DELETE )
         return;

      // pass only the first dot
      if( ch == dsep && (getText().indexOf(dsep) < 0) ) 
         return;

      // reject everything else
      ev.consume();
   }

   // add/remove methods for KeyListener not needed (provided by Component)
}