public class Lexer
{
   String derString;
    
   public Lexer()
   {
      derString = "";
   }
	
   private boolean istZiffer(char c)
   {
      return (('0' <= c) && (c <= '9'));
   }

   private boolean istVorzeichen(char c)
   {
      return ((c == '+') || (c == '-'));
   }
  
   public boolean istInt(String s)
   {
      int q;
      char c;
  
      q = 1;
      while (s.length() > 0)
      {
         c = s.charAt(0);
         if (q == 1)
         { 
            if (istVorzeichen(c)) q = 2; else
            if (istZiffer(c))     q = 3; else q = 99;
         }
         else if ((q == 2) || (q == 3))           
         {
            if (istZiffer(c))     q = 3; else q = 99;
         }
         s = s.substring(1);
      }
      return (q==3);
   }
}