Ultrasimplistic example of a mini/micro compiler that validates a sentence starting with "hombres" and finishing with "tal"

Main.java

import java.text.ParseException;
class Lexer { 
    String [] tokens;
    void tokenize( String input ) { 
       tokens = input.split("\\s");
    }
}
class Parser {
   void parse( String [] tokens ) throws ParseException { 
      // la regla es que empieze con "hombres" y termine con "tal" 
        if (   tokens == null 
            || tokens.length == 0 
            || !tokens[0].equals("hombres") 
            || !tokens[tokens.length-1].equals("tal") ) { 
                        throw new ParseException("<hombres> expected at the beginning or <tal> at the end."+tokens[tokens.length-1], 0);
      }
       /// todo ok       
  } 
}

class CodeGenerator { 
     String [] transform( String [] tokens ) { 
         String [] output = new String[tokens.length];
         int i = 0;
         StringBuilder sb = new StringBuilder();
         for ( String token : tokens ) { 
             output[i++] = sb.append(token).reverse().toString();
             sb.setLength(0);
         }
         return output;
     }
}
class Main {
    public static void main( String ... args ) throws ParseException { 
        Lexer l = new Lexer();
        l.tokenize( args[0] );
        Parser p = new Parser();
        p.parse( l.tokens );
        CodeGenerator g = new CodeGenerator();
        for ( String s : g.transform( l.tokens ) ) { 
            System.out.print(s);
            System.out.print(' ');
        }
        System.out.println();
    }
}

i have a Java error: Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0
at l.tokenize( args[0] );

how can i fix it??