import java.util.Scanner;

/**
*
* @author xingyu
*/
public class Calculator {

public static void main(String[] args) {
   Scanner input = new Scanner(System.in);
   String line;
   StackCalc calc = new StackCalc();
   while (input.hasNextLine()) {
         line = input.nextLine();
         processing(line, calc);
   }
}

/**
* process each line
* @param line
* @param calc
*/
private static void processing(String line, StackCalc calc) {

   // split line by spaces
   String[] sp = line.split("\\s+");
   if (sp.length > 2 || sp.length < 1) {
         System.err.println("Invalid command: " + line);
         return;
   }

   try {
         if (sp.length == 1) {
            if (sp[0].equals("add")) {
               System.out.println(calc.add());
            } else if (sp[0].equals("multiply")) {
               System.out.println(calc.multiply());
            } else {
               System.err.println("Invalid command: " + line);
            }
         } else {
            if (sp[0].equals("push")) {
               calc.push(sp[1]);
            } else {
               System.err.println("Invalid command: " + line);
            }
         }
   } catch (Exception e) {
         System.err.println(e.getMessage());
   }
}
}

Programming Assignment 5 â€“ Golf Course A company wants to invest...