How to store numbers in a stack....

Question

hello guys...i ve got the following assignment:
Write a Java program that reads and evaluates a fully parenthesised arithmetic expression. The
purpose of this program is to illustrate a fundamental use of stacks. Implement the stack using
Linked Lists as explained in your notes.
For e.g if a user enters the expression: (((6 + 9) / 3) * (6 � 4))
The result should be 10.
Your program should be properly documented and well structured. Specifications should be
clearly written in your logbook for all the methods, constructors, and classes that you implement
in the following format:
Class / Method/ Constructor name explaining what it does
Parameters
Preconditions
Postconditions
Throws
Now, i ve come up with the following code:
import java.util.EmptyStackException;
class StackNode {
     private static Object data;
     private StackNode link;
     private static StackNode head;
     private int totalnodes;
// the constructors
public StackNode(Object obj, StackNode lk)
     data = obj;
     link = lk;
public StackNode()
     head = null;
     totalnodes = 0;
     // the push method
     public void push(Object obj)
          head = new StackNode(obj, head);
          totalnodes++;
     // the pop method
     public Object pop()
          Object answer;
          if(head == null)
               throw new EmptyStackException();
          answer = head.getData();
          head = head.getLink();
          totalnodes--;
          return answer;
     // the isEmpty method
     public boolean isEmpty()
          return (head == null);
     // get data
     public Object getData()
          return data;
     // get link
     public StackNode getLink()
          return link;
     // size or length method
     public int size()
          return totalnodes;
     public static void main (String args [])
          int i;
          StackNode number = new StackNode();
          StackNode operator = new StackNode();
          head = new StackNode(data, head);
          number.push(new Integer(9));
          number.push(new Integer(6));
          operator.push(new Character('+'));
and i dont know how to store numbers into the stack and how to use the operations such as addition substraction division and multiply...
any ideas how to do that??
cheers....

Answer 1

This doesn't use a stack but the concept is the same:
import java.util.*;
public class formula {
public  int aValue = 1;
public  int bValue = 2;
public  int cValue = 3;
public formula() {
   //StringTokenizer st = new StringTokenizer("a + b/c", " abc()+-*/", true);
   //while (st.hasMoreTokens()) { System.out.println(st.nextToken()); }
   StringTokenizer st2 = new StringTokenizer("a + (c - b) + (b * c)", " abc()+-*/", true);
  int operand1 = 0;
  int operand2 = 0;
  int operator = 0;
  //flag: first operand has a value
  boolean firstOperandFull = false;
  //flag: second operand has a value
  boolean secondOperandFull = false;
  //flag: tokens are between parens
  boolean inParens = false;
  Vector inParensVector = null;
  MAINLOOP:
    while (st2.hasMoreTokens()) {
              String x = st2.nextToken();
              //if token is a blank skip it.
              if (x.equals(" ")) { continue MAINLOOP; }
              System.out.println(x);
              //if token is open parens set flag and skip to next token
              if (x.equals("(")) { inParens = true; inParensVector = new Vector(); continue MAINLOOP; }
              //if tokn is close parens, retrieve the value from between the parens and reset flag.
              if (x.equals(")")) { if (! firstOperandFull) { operand1 = doInParens(inParensVector); firstOperandFull = true; }
                                   else { operand2 = doInParens(inParensVector); secondOperandFull = true;  }
                                   inParensVector = null; inParens = false; }
              //if token is open parens store all tokens until close else process the token
              if (inParens) { inParensVector.add(x); }
              else {
                   //if token is a variable put correct value in operand
                   if (x.equals("a")) { if (! firstOperandFull) { operand1 = aValue; firstOperandFull = true; }
                                        else { operand2 = aValue; secondOperandFull = true;  } }
                   if (x.equals("b")) { if (! firstOperandFull) { operand1 = bValue; firstOperandFull = true; }
                                        else { operand2 = bValue; secondOperandFull = true;  } }
                   if (x.equals("c")) { if (! firstOperandFull) { operand1 = cValue; firstOperandFull = true; }
                                        else { operand2 = cValue; secondOperandFull = true;  } }
                   //if token is a operator store the operation
                   if (x.equals("+")) { if (firstOperandFull) { operator = 1; } }
                   if (x.equals("-")) { if (firstOperandFull) { operator = 2; } }
                   if (x.equals("*")) { if (firstOperandFull) { operator = 3; } }
                   if (x.equals("/")) { if (firstOperandFull) { operator = 4; } }
                   System.out.println("operand1 = " + operand1 + " operand2 = " + operand2 + " operator = " + operator);
                    //if second operand has a value perform the operation.
                   if (secondOperandFull) {
                                           switch (operator) {
                                                    case 1 : operand1 = add(operand1, operand2); secondOperandFull = false; break;
                                                    case 2 : operand1 = subtract(operand1, operand2); secondOperandFull = false; break;
                                                    case 3 : operand1 = multiply(operand1, operand2); secondOperandFull = false; break;
                                                    case 4 : operand1 = divide(operand1, operand2); secondOperandFull = false; break;
                                                    }//end switch
                                             } //end if
                 } //End inParens else
  } //End while
System.out.println("answer = " + operand1);
public static void main(String[] args) { //formula f = new formula();
Vector v = new Vector();
StringTokenizer st = new StringTokenizer(",Greg,,Paul,,", ",", true);
String token = null;
String lastToken = " ";
boolean firstToken = true;
while (st.hasMoreTokens()) {
token = st.nextToken();
if (firstToken) { if (token.equals(",")) { v.add("X"); }
firstToken = false; }
if (! token.equals(",")) { v.add(token); }
else { if (lastToken.equals(",")) { v.add("X"); } }
lastToken = token;
} //End While
if (token.equals(",")) { v.add("X"); }
Enumeration tokens = v.elements();
while (tokens.hasMoreElements()) {
      System.out.println((String)tokens.nextElement()); }
} //End Main
public int add(int operand1, int operand2) { return operand1 + operand2; }
public int subtract(int operand1, int operand2) { return operand1 - operand2; }
public int divide(int operand1, int operand2) { return operand1 / operand2; }
public int multiply(int operand1, int operand2) { return operand1 * operand2; }
public int doInParens(Vector inParensVector) {
      int operand1 = 0;
      int operand2 = 0;
      int operator = 0;
      boolean firstOperandFull = false;
      boolean secondOperandFull = false;
      Enumeration tokens = inParensVector.elements();
      INPARENSLOOP:
           while (tokens.hasMoreElements()) {
              String x = (String)tokens.nextElement();
              //if token is a blank skip it.
              if (x.equals(" ")) { continue INPARENSLOOP; }
              System.out.println("inparens : " + x);
              //if token is a variable put correct value in operand
                  if (x.equals("a")) { if (! firstOperandFull) { operand1 = aValue; firstOperandFull = true; }
                                      else { operand2 = aValue; secondOperandFull = true;  } }
              if (x.equals("b")) { if (! firstOperandFull) { operand1 = bValue; firstOperandFull = true; }
                                  else { operand2 = bValue; secondOperandFull = true;  } }
              if (x.equals("c")) { if (! firstOperandFull) { operand1 = cValue; firstOperandFull = true; }
                                       else { operand2 = cValue; secondOperandFull = true;  } }
             //if token is a operator store the operation
             if (x.equals("+")) { if (firstOperandFull) { operator = 1; } }
              if (x.equals("-")) { if (firstOperandFull) { operator = 2; } }
             if (x.equals("*")) { if (firstOperandFull) { operator = 3; } }
             if (x.equals("/")) { if (firstOperandFull) { operator = 4; } }
              System.out.println("Inparens : operand1 = " + operand1 + " operand2 = " + operand2 + " operator = " + operator);
             if (secondOperandFull) {
                                     switch (operator) {
                                               case 1 : operand1 = add(operand1, operand2); secondOperandFull = false; break;
                                                   case 2 : operand1 = subtract(operand1, operand2); secondOperandFull = false; break;
                                                   case 3 : operand1 = multiply(operand1, operand2); secondOperandFull = false; break;
                                                   case 4 : operand1 = divide(operand1, operand2); secondOperandFull = false; break;
                                                   }//end switch
                                     } //end if
              } //End while
           System.out.println("Inparens return = " + operand1);
           return  operand1;
}//End doInParens
}//End Class