/** Program 6.10 The PostfixInterpreter Class That Evaluates a Postfix String */

class PostfixInterpreter {
    
   private String postfixString, outputString;
 
   /*----------------------------------------*/
    
   private boolean isOperator(char c) {
    
     return (c == '+'  ||  c == '-'  ||  c == '*'  ||  c == '/'  ||  c == '^');
   
   }//end isOperator
    
   /*----------------------------------------*/
    
   private boolean isSpace(char c) {
    
     return (c == '  ');
   
   }//end isSpace
 
   /*----------------------------------------*/
    
   public void interpretPostfix() {
    
     Stack evalStack = new Stack();
    
     double leftOperand, rightOperand;
 
     char c;
   
     StringTokenizer parser = new StringTokenizer(postfixString,"+-*/^  ",true);
 
     while (parser.hasMoreTokens()) {         // provided there are more
                                          // tokens in the postfixString
       String token = parser.nextToken();          // get the next token
                                                         // and let c be
       c = token.charAt(0);         // the first character of this token
   
       if ( (token.length() == 1) && isOperator(c) ) {    // if token is
                                                         //  an operator
         rightOperand = ((Double)evalStack.pop()).doubleValue();
         leftOperand = ((Double)evalStack.pop()).doubleValue();
     
         switch (c) {                            // perform the operation
     
          case '+': evalStack.push(new Double(leftOperand+rightOperand));
                    break;
          case '-': evalStack.push(new Double(leftOperand-rightOperand));
                    break;
          case '*': evalStack.push(new Double(leftOperand*rightOperand));
                    break;
          case '/': evalStack.push(new Double(leftOperand/rightOperand));
                    break;
          case '^': evalStack.push(new Double(Math.exp(
                    Math.log(leftOperand)*rightOperand) ) );
                    break;
          default:
                    break;
         }//end switch
   
       } else if ( (token.length() == 1) && isSpace(c) ) {    // else if
                                                    // token was a space
         ;                                                  // ignore it
   
       } else {                   // otherwise, push the numerical value
                                                         // of the token
         evalStack.push(Double.valueOf(token));          // on the stack
   
       }//end if
 
     }//end while
 
     // remove final result from stack and output it
 
        output("Value of postfix expression = " + evalStack.pop() );
   
   }//end interpretPostfix
    
 /*----------------------------------------*/
 
   private void output(String s) {
 
     outputString = s;
 
   }//end output
    
 /*----------------------------------------*/
    
   public void setInput(String input) {
 
     postfixString = input;
 
   }//end setInput
 
 /*----------------------------------------*/
   
   public String getOutput() {
    
     return outputString;
   
   }//end getOutput
    
 /*----------------------------------------*/
   
}//end class PostfixInterpreter

/* insert here the Stack class given either in Program 6.11 or 6.12 */


/*--------------------------------------------------------------------------*/