Implementing order of operations for a Java calculator.

How would I go about implementing order of operations for a calculator program that takes input from its GUI and stores it for further processing in the form of Strings?

ETA: I accidentally hit the "Submit thread" button; I will be posting code shortly.

I already have some code that implements order of operations without algebraic grouping (i.e., parentheses/bracket):

Code Java:

---

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Stack;
import javax.swing.JTextField;
import java.lang.*;
 
public class ArithmeticListener implements ActionListener
{
    boolean optPsh = false;
    boolean pntPsh = false;
    double fOpd;
    double sOpd;
    double res;
    String ariStr = "";
    String digStr = "";
    String pntStr = "";
    String opdStr = "";
    String curOpdStr = "";
    String prvOpdStr = "";
    String curOptStr = "";
    String prvOptStr = "";
    Stack<String> expStck = new Stack<String> ();
    Stack<String> opdStck = new Stack<String> ();
    Stack<String> optStck = new Stack<String> ();
    JTextField scrn;
 
    ArithmeticListener(CalculatorGUI calGUI)
    {
        scrn = calGUI.cs.screen;
    }
 
    public void actionPerformed(ActionEvent ae)
    {
        ariStr = ae.getActionCommand();
        opdStr = scrn.getText();
 
        /*Operand entry omitted for brevity*/
 
        if (ariStr.equals("+") || ariStr.equals("-"))
        {
            curOptStr = ariStr;
            curOpdStr = scrn.getText();
 
            optPsh = true;
            pntPsh = false;
 
            if (opdStck.empty() && optStck.empty())
            {
                opdStck.push(curOpdStr);
                optStck.push(curOptStr);
            }
            else
            {
                if (opdStck.size() == 1 && optStck.size() == 1)
                {
                    prvOptStr = optStck.pop();
                    prvOpdStr = opdStck.pop();
 
                    sOpd = Double.parseDouble(curOpdStr);
                    fOpd = Double.parseDouble(prvOpdStr);
 
                    if (prvOptStr.equals("+"))
                    {
                        res = fOpd + sOpd;
                    }
                    else if (prvOptStr.equals("-"))
                    {
                        res = fOpd - sOpd;
                    }
                    else if (prvOptStr.equals("*"))
                    {
                        res = fOpd * sOpd;
                    }
                    else if (prvOptStr.equals("/"))
                    {
                        res = fOpd / sOpd;
                    }                                    
                opdStck.push(res + "");
                optStck.push(curOptStr);
                scrn.setText(res + "");
                }
                else
                {
                    while (opdStck.size() > 0 && optStck.size() > 0)
                    {
                        prvOptStr = optStck.pop();
                        prvOpdStr = opdStck.pop();
 
                        sOpd = Double.parseDouble(curOpdStr);
                        fOpd = Double.parseDouble(prvOpdStr);
 
                        if (prvOptStr.equals("+"))
                        {
                            res = fOpd + sOpd;
                        }
                        else if (prvOptStr.equals("-"))
                        {
                            res = fOpd - sOpd;
                        }
                        else if (prvOptStr.equals("*"))
                        {
                            res = fOpd * sOpd;
                        }
                        else if (prvOptStr.equals("/"))
                        {
                            res = fOpd / sOpd;
                        }
                        curOpdStr = (res + "");
 
                        for (String s : opdStck)
                        {
                            System.out.print(s);
                        }
                        System.out.println();
                        for (String s : optStck)
                        {
                            System.out.print(s);
                        }
                        System.out.println();
                        System.out.println();
 
                    }
                opdStck.push(res + "");
                optStck.push(curOptStr);
                scrn.setText(res + "");
                }
            }
        }
        else if (ariStr.equals("*")|| ariStr.equals("/"))
        {
            curOptStr = ariStr;
            curOpdStr = scrn.getText();
 
            optPsh = true;
            pntPsh = false;
 
            if (opdStck.empty() && optStck.empty())
            {
                opdStck.push(curOpdStr);
                optStck.push(curOptStr);
            }
            else
            {
                if (opdStck.size() == 1 && optStck.size() == 1)
                {
                    prvOptStr = optStck.pop();
                    prvOpdStr = opdStck.pop();
 
                    if (prvOptStr.equals("+") || prvOptStr.equals("-"))
                    {
                        opdStck.push(prvOpdStr);
                        optStck.push(prvOptStr);
                        opdStck.push(curOpdStr);
                        optStck.push(curOptStr);
                    }
                    else if (prvOptStr.equals("*") || prvOptStr.equals("/"))
                    {
                        sOpd = Double.parseDouble(curOpdStr);
                        fOpd = Double.parseDouble(prvOpdStr);
 
                        if (prvOptStr.equals("*"))
                        {
                            res = fOpd * sOpd;
                        }
                        else if (prvOptStr.equals("/"))
                        {
                            res = fOpd / sOpd;
                        }
                        opdStck.push(res + "");
                    }                    
                }
                else
                {
                    opdStck.push(curOpdStr);
                    optStck.push(curOptStr);
                }
            }
        }
        else if (ariStr.equals("="))
        {
                    while (opdStck.size() > 0 && optStck.size() > 0)
                    {
                        prvOptStr = optStck.pop();
                        prvOpdStr = opdStck.pop();
 
                        sOpd = Double.parseDouble(curOpdStr);
                        fOpd = Double.parseDouble(prvOpdStr);
 
                        if (prvOptStr.equals("+"))
                        {
                            res = fOpd + sOpd;
                        }
                        else if (prvOptStr.equals("-"))
                        {
                            res = fOpd - sOpd;
                        }
                        else if (prvOptStr.equals("*"))
                        {
                            res = fOpd * sOpd;
                        }
                        else if (prvOptStr.equals("/"))
                        {
                            res = fOpd / sOpd;
                        }
                        curOpdStr = (res + "");
                    }
                opdStck.push(res + "");
                optStck.push(curOptStr);
                scrn.setText(res + "");
 
        }
        else if (ariStr.equals("C"))
        {
            while (!opdStck.empty() && !optStck.empty())
            {
                optStck.pop();
                opdStck.pop();
            }
 
            optPsh = false;
            pntPsh = false;
            fOpd = 0;
            sOpd = 0;
            res = 0;
            ariStr = "";
            digStr = "";
            opdStr = "";
            curOpdStr = "";
            prvOpdStr = "";
            curOptStr = "";
            prvOptStr = "";
 
            scrn.setText("0");
        }
    }
}

---

Now, the way I see things, I have two options:

1. Add a parenthesis Stack to the current method
2. Get rid of the operator Stack and the operand Stack and just have an expression Stack

The latter option seems to be more straightforward because I don't have to come up with a way to "sync" up to the Stacks in order to keep track of where the parentheses are entered.

The problem that I am currently having, though, is that, when I enter an open parenthesis, the previous operand is pushed onto the Stack as well. I think that this is happening because I have misplaced a call to the screen's getText() method and the operand text on the screen is getting pushed onto the the Stack
with the open parenthesis. However, I cannot justify this thought when I look at the code:

Code Java:

---

import java.awt.event.*;
import java.util.*;
import javax.swing.*;
 
public class Dummy implements ActionListener
{
    boolean optPsh = false;
    boolean pntPsh = false;
    int numOpnPar;
    double fOpd;
    double sOpd;
    double res;
    String ariStr = "";
    String digStr = "";
    String pntStr = "";
    String opdStr = "";
    String curOpdStr = "";
    String prvOpdStr = "";
    String curOptStr = "";
    String prvOptStr = "";
    Stack<String> expStck = new Stack<String> ();
    Stack<String> opdStck = new Stack<String> ();
    Stack<String> optStck = new Stack<String> ();
    JTextField scrn;
 
    Dummy(CalculatorGUI cg)
    {
        scrn = cg.cs.screen;
    }
 
    public void actionPerformed(ActionEvent ae)
    {
        ariStr = ae.getActionCommand();
        char [] ariChrArr = ariStr.toCharArray();
        opdStr = scrn.getText();
        Character ariChr = ariChrArr[0];
 
        System.out.println("ariChr: " + ariChr);
 
        if (!ariStr.equals("C") && !ariStr.equals("CE"))
        {
            if (isOpd(ariChr))
            {
            	System.out.println("Operand Character");
                if(!optPsh)
                {
                	if (!pntPsh)
                	{
                		if (opdStr.equals("0"))
                		{
                	        if (Character.isDigit(ariChr))
                	        {
                	        	opdStr = ariStr;
                	        }
                	        else if (ariStr.equals("."))
                	        {
                	        	opdStr = "0" + ariStr;
                	        	pntPsh = true;
                	        }
                		}
            	        else
                		{
                	        if (Character.isDigit(ariChr))
                	        {
                	        	opdStr += ariStr;
                	        }
                	        else if (ariStr.equals("."))
                	        {
                	        	opdStr += ariStr;
                	        	pntPsh = true;
                	        }
                		}
                	}
                	else
                	{
            	        if (Character.isDigit(ariChr))
            	        {
            	        	opdStr += ariStr;
            	        }
            	        else if (ariStr.equals("."))
            	        {
            	        	opdStr += ariStr;
            	        	pntPsh = true;
            	        }
                	}
                }
                else
                {
                	if (!pntPsh)
                	{
                		if (opdStr.equals("0"))
                		{
                	        if (Character.isDigit(ariChr))
                	        {
                	        	opdStr = ariStr;
                	        }
                	        else if (ariStr.equals("."))
                	        {
                	        	opdStr = "0" + ariStr;
                	        	pntPsh = true;
                	        }
                		}
            	        else
                		{
                	        if (Character.isDigit(ariChr))
                	        {
                	        	opdStr = ariStr;
                	        }
                	        else if (ariStr.equals("."))
                	        {
                	        	opdStr = "0" + ariStr;
                	        	pntPsh = true;
                	        }
                		}
                	}
                	optPsh = false;
                }
                scrn.setText(opdStr);
                ariStr = "";
            }
            else
            {
            	curOptStr = ariChr.toString();
 
            	optPsh = true;
 
            	if (curOptStr.equals("("))
            	{
            		expStck.push(curOptStr);
            	}
            	if (curOptStr.equals(")"))
            	{
            		expStck.push(curOptStr);
            	}
            	else
            	{
                	curOpdStr = scrn.getText();
            		expStck.push(curOpdStr);
            		expStck.push(curOptStr);
            	}
            	System.out.print("expStck: ");
            	prntExprStck(expStck);
 
            	curOpdStr = "";
            	curOptStr = "";
            }
        }
        else if (ariStr.equals("C"))
        {
            while (!expStck.empty())
            {
            	expStck.pop();
            }
            scrn.setText("0");
            optPsh = false;
            pntPsh = false;
            fOpd = 0;
            sOpd = 0;
            res = 0;
            ariStr = "";
            digStr = "";
            pntStr = "";
            opdStr = "";
            curOpdStr = "";
            prvOpdStr = "";
            curOptStr = "";
            prvOptStr = "";
        }
        else if (ariStr.equals("CE"))
        {
            scrn.setText("0");
        }
    }
 
    boolean isOpd(Character chr)
    {
    	if (Character.isDigit(chr) || chr == '.')
    	{
    		return true;
    	}
    	else
    	{
    		return false;
    	}
    }
}

---

Am I completely missing something else I have not mentioned?

Since a lot of your code is missing, the only thing I can suggest is to add some print statements to your code to display variables as they change and to trace execution flow.