Infix to Postfix using Stacks

[greyfox32]

I am working on a project for class. I have to write a program that reads in an infix expression and converts and it to postfix and evaluates it. Currently I have it to where I can convert an infix expression with no parentheses to postfix, but am having some trouble figuring out how to handle parentheses.

import java.util.*;


public class InfToPost
{
    private Stack<String> convStack;
    private Stack<String> evalStack;
    private String infixExp;
    private String postfixExp = "";
    private int temp;
    private int result;

    public InfToPost(String exp)
    {
        String str = "";
        infixExp = exp;
        convStack = new Stack<String>();
        evalStack = new Stack<String>();

        for(int i = 0; i < infixExp.length(); i++)
        {
            str = infixExp.substring(i,i+1);
            if(str.matches("[A-Z]|\\d"))
            {
                postfixExp += str;

            }
            else if(isOperator(str))
            {
                if(convStack.isEmpty())
                {
                    convStack.push(str);
                }
                else
                {
                    String StackTop = convStack.peek();
                    while(getPrecedence(StackTop,str).equals(StackTop) && !(convStack.isEmpty()))
                    {
                        postfixExp += convStack.pop();
                        if(!(convStack.isEmpty()))
                        {
                            StackTop = convStack.peek();
                        }
                    }
                    convStack.push(str);
                }
            }
        }
        while(!(convStack.isEmpty()))
        {
            postfixExp += convStack.pop();
        }


        System.out.println("Infix:" +" " + infixExp + "\n" + "Postfix:" + " " + postfixExp + "\n" + "Result:" +result);
    }

    private boolean isOperator(String ch)
    {
        String operators = "*/%+-";
        if(operators.indexOf(ch) != -1)
        {
            return true;
        }
        else
        {
            return false;
        }
    }

    private String getPrecedence(String op1, String op2)
    {
        String addSub = "+-";
        String mulDiv = "*/";

        if ((mulDiv.indexOf(op1) != -1) && (addSub.indexOf(op2) != -1))
        {
            return op1;
        }
        else if ((mulDiv.indexOf(op2) != -1) && (addSub.indexOf(op1) != -1))
        {
            return op2;
        }
        else if((mulDiv.indexOf(op1) != -1) && (mulDiv.indexOf(op2) != -1))
        {
            return op1;
        }
        else 
        {       
            return op1;
        }
    }

    public static void main(String[] args)
    {

        Scanner scanner = new Scanner(System.in);

        String expression = scanner.nextLine();
        new InfToPost(expression);
    }
}