public void allow(Variable optVariable){
  if (null == allowedVariables) {
    allowedVariables=new Hashtable();
  }
  if (null != optVariable)   allowedVariables.put(optVariable,optVariable);
}

public void allow ( Variable optVariable ) { if ( null == allowedVariables ) { allowedVariables = new Hashtable ( ) ; } if ( null != optVariable ) allowedVariables . put ( optVariable , optVariable ) ; }
adjust the set of allowed variables : create it ( if not yet existent ) and add optvariable ( if it ' s nonnull ) . if the allowed - variable set exists , the parser will reject input strings that use any other variables .
