Pop from stack and store to char?

Question

I am trying to write an infix to postfix prgm and when i compile i get:
ListOperations3.java:143: incompatible types
found : java.lang.Object
required: char
topOp = oStack.pop();
because apparently the built in stacks use generic objects as a return type and thats incompatible with char. How can i pop from the stack to a char?
Here is a method where the problem arises:
public void Parenthesis(){
char ch;
char topOp;
while(!oStack.isEmpty()){
topOp = oStack.pop();
if(ch == '(')
break;
else
postFix = postFix + ch;
}

Answer 1

This is one of the classes that contains the options for a menu. The other two classes dont have any real
impact on the code so I'm not gonna post them.
import java.util.*;
  import java.io.*;
  import javax.swing.*;
  import java.lang.*;
    public class ListOperations3{
      public String postFix = "";  
      public String expression = "";
      Scanner scan;
      Stack oStack = new Stack();
      char ch;
       public ListOperations3(Scanner scan){
         this.scan  = scan;
       public void menu(){
         char option;
         String message;
         int score;
         Screen scr = new Screen ();
         scr.clearscreen ();
         scr.movedown (10);
         DisplayMenu3 menu = new DisplayMenu3();
         menu.printmenu ();
         do {
            scr.movedown (2);
            scr.moveright (15);
            System.out.print ("Enter an option: 0 for Menu, Q to quit");
            message = scan.next();
            option = message.charAt(0);
            switch (option) {
               case '0':     scr.clearscreen ();
                  scr.movedown (10);
                  menu.printmenu ();
                  break;                           
               case '1': //Accept infix expression from user
                  expression = JOptionPane.showInputDialog("Please enter an expression using variables(A-Z):\t");
                  expression = expression.toUpperCase();
                  expression = expression.replaceAll(" ", "");
                  break;                           
               case '2':// Convert to postfix expression
                  scr.clearscreen ();
                  String postfix = InToPost(expression); 
               case '3': // Evaluate postfix expression
                  break;                           
               case 'q':   
                  break;
               case 'Q':  
                  break;    
               default:     scr.clearscreen ();
                  scr.movedown (10);
                  scr.moveright (15);
                  System.out.println ("Invalid option");
                  scr.movedown (5);
                  menu.printmenu ();
                  break;
            }// switch
         } // do
         while (option != 'Q'&& option != 'q');
         scr.clearscreen ();
         scr.movedown (10);
         scr.moveright (15);
         System.out.println("Thank you for using this program ");
         scr.movedown (3);
         scr.moveright (15);
         System.out.println("Have a nice day");
      } // main method             
       public String InToPost(String infix){
         for (int i = 0; i < infix.length(); i++) {
            ch = infix.charAt(i);
            switch(ch){                    
               case '+'://It's addition
                  Operator(ch, 1);
                  break;
               case '-'://It's subtraction
                  Operator(ch, 1);
                  break;                            
               case '*'://It's multiplication
                  Operator(ch, 2);
                  break;
               case '/'://It's division
                  Operator(ch, 2);
                  break;                            
               case '^'://It's exponential
                  Operator(ch, 3);
                  break;                            
               case '('://It's a left parenthesis
                  oStack.push(new Character(ch));
                  break;                            
               case ')'://It's a right parenthesis
                  Parenthesis();
                  break;                            
               default://It's an operand
                  postFix = postFix + ch;
                  break;                                    
         return postFix;
       public void Operator(char thisOp, int thisPrec){
         int topPrec;
            char topOp;
         while (!oStack.isEmpty()){
           Character c = oStack.pop();
            topOp = c.charValue();           
            if(topOp == '('){
               oStack.push(new Character(topOp));
               break;
            else {
               if(topOp == '+' || topOp == '-')
                  topPrec = 1;
               else if(topOp == '*' || topOp == '/')
                  topPrec = 2;
               else if(topOp == '^')
                  topPrec = 3;
               if(topPrec < thisPrec){
                  oStack.push(new Character(topOp));
                  break;
               else
                  postFix = postFix + topOp;
         oStack.push(new Character(topOp));   
       public void Parenthesis(){
            char topOp;
         while(!oStack.isEmpty()){
           Character c = oStack.pop();
            topOp = c.charValue();
            if(topOp == '(')
               break;
            else
               postFix = postFix + topOp;
   }// class NewBasicMenu <code class="jive-code jive-java">