Confused about string that I think shouldn't be null
I am trying to write a basic four-function calculator. Here is the code:
Code Java:
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.swing.*;
import javax.swing.event.*;
class SingleObjectCalculator extends JFrame
{
JTextField screen = new JTextField("0",15);
JButton one;
JButton two;
JButton three;
JButton four;
JButton five;
JButton six;
JButton seven;
JButton eight;
JButton nine;
JButton zero;
JButton point;
JButton plus;
JButton minus;
JButton times;
JButton divide;
JButton equals;
JButton clear;
Stack<String> opndStck = new Stack<String>();
Stack<String> optrStck = new Stack<String>();
class ButtonListener implements ActionListener
{
boolean ptPshd = false;
boolean optrPshd = false;
double fOpnd = 0;
double sOpnd = 0;
double res = 0;
String exprStr = "";
String optrStr = "";
String curOpndStr = "";
String prvOpndStr = "";
String curOptrStr = "";
String prvOptrStr = "";
String prvPrvOptrStr = "";
public void actionPerformed (ActionEvent ae)
{
String butStr = ae.getActionCommand();
if (butStr.equals("0"))
{
if (!optrPshd)
{
if (exprStr.equals("0"))
{
exprStr = butStr;
screen.setText(exprStr);
}
}
else
{
exprStr = butStr;
}
optrPshd = false;
}
else if (butStr.equals("1"))
{
if (!optrPshd)
{
if (exprStr.equals("0"))
{
exprStr = butStr;
screen.setText(exprStr);
}
else
{
exprStr += butStr;
screen.setText(exprStr);
}
}
else
{
if (exprStr.length() != 0)
{
exprStr = butStr;
screen.setText(exprStr);
}
else
{
exprStr += butStr;
screen.setText(exprStr);
}
optrPshd = false;
}
}
else if (butStr.equals("2"))
{
if (!optrPshd)
{
if (exprStr.equals("0"))
{
exprStr = butStr;
screen.setText(exprStr);
}
else
{
exprStr += butStr;
screen.setText(exprStr);
}
}
else
{
if (exprStr.length() != 0)
{
exprStr = butStr;
screen.setText(exprStr);
}
else
{
exprStr += butStr;
screen.setText(exprStr);
}
optrPshd = false;
}
}
else if (butStr.equals("3"))
{
if (!optrPshd)
{
if (exprStr.equals("0"))
{
exprStr = butStr;
screen.setText(exprStr);
}
else
{
exprStr += butStr;
screen.setText(exprStr);
}
}
else
{
if (exprStr.length() != 0)
{
exprStr = butStr;
screen.setText(exprStr);
}
else
{
exprStr += butStr;
screen.setText(exprStr);
}
optrPshd = false;
}
}
else if (butStr.equals("4"))
{
if (!optrPshd)
{
if (exprStr.equals("0"))
{
exprStr = butStr;
screen.setText(exprStr);
}
else
{
exprStr += butStr;
screen.setText(exprStr);
}
}
else
{
if (exprStr.length() != 0)
{
exprStr = butStr;
screen.setText(exprStr);
}
else
{
exprStr += butStr;
screen.setText(exprStr);
}
optrPshd = false;
}
}
else if (butStr.equals("5"))
{
if (!optrPshd)
{
if (exprStr.equals("0"))
{
exprStr = butStr;
screen.setText(exprStr);
}
else
{
exprStr += butStr;
screen.setText(exprStr);
}
}
else
{
if (exprStr.length() != 0)
{
exprStr = butStr;
screen.setText(exprStr);
}
else
{
exprStr += butStr;
screen.setText(exprStr);
}
optrPshd = false;
}
}
else if (butStr.equals("6"))
{
if (!optrPshd)
{
if (exprStr.equals("0"))
{
exprStr = butStr;
screen.setText(exprStr);
}
else
{
exprStr += butStr;
screen.setText(exprStr);
}
}
else
{
if (exprStr.length() != 0)
{
exprStr = butStr;
screen.setText(exprStr);
}
else
{
exprStr += butStr;
screen.setText(exprStr);
}
optrPshd = false;
}
}
else if (butStr.equals("7"))
{
if (!optrPshd)
{
if (exprStr.equals("0"))
{
exprStr = butStr;
screen.setText(exprStr);
}
else
{
exprStr += butStr;
screen.setText(exprStr);
}
}
else
{
if (exprStr.length() != 0)
{
exprStr = butStr;
screen.setText(exprStr);
}
else
{
exprStr += butStr;
screen.setText(exprStr);
}
optrPshd = false;
}
}
else if (butStr.equals("8"))
{
if (!optrPshd)
{
if (exprStr.equals("0"))
{
exprStr = butStr;
screen.setText(exprStr);
}
else
{
exprStr += butStr;
screen.setText(exprStr);
}
}
else
{
if (exprStr.length() != 0)
{
exprStr = butStr;
screen.setText(exprStr);
}
else
{
exprStr += butStr;
screen.setText(exprStr);
}
optrPshd = false;
}
}
else if (butStr.equals("9"))
{
if (!optrPshd)
{
if (exprStr.equals("0"))
{
exprStr = butStr;
screen.setText(exprStr);
}
else
{
exprStr += butStr;
screen.setText(exprStr);
}
}
else
{
if (exprStr.length() != 0)
{
exprStr = butStr;
screen.setText(exprStr);
}
else
{
exprStr += butStr;
screen.setText(exprStr);
}
optrPshd = false;
}
}
else if (butStr.equals("."))
{
if (!ptPshd)
{
if (!optrPshd)
{
if (exprStr.equals("0"))
{
exprStr += butStr;
screen.setText(exprStr);
}
else
{
exprStr += butStr;
screen.setText(exprStr);
}
}
else
{
if (exprStr.length() != 0)
{
exprStr = ("0" + butStr);
screen.setText(exprStr);
}
else
{
exprStr += butStr;
screen.setText(exprStr);
}
optrPshd = false;
}
}
ptPshd = false;
}
else if (butStr.equals("+"))
{
optrStr = butStr;
ptPshd = false;
if (!optrPshd)
{
if (opndStck.empty() && optrStck.empty())
{
opndStck.push(screen.getText());
optrStck.push(optrStr);
}
else if (!opndStck.empty() && !optrStck.empty())
{
curOpndStr = screen.getText();
curOptrStr = optrStr;
}
optrPshd = true;
}
else
{
optrStck.pop();
optrStck.push(optrStr);
}
if (opndStck.size() > 0 && optrStck.size() > 0)
{
prvOpndStr = opndStck.pop();
prvOptrStr = optrStck.pop();
sOpnd = Double.parseDouble(curOpndStr);
fOpnd = Double.parseDouble(prvOpndStr);
System.out.println(sOpnd);
System.out.println(fOpnd);
while (opndStck.size() > 1 && optrStck.size() > 1)
{
if (opndStck.size() == 1 && optrStck.size() == 1)
{
if (prvOptrStr.equals("+"))
{
res = fOpnd + sOpnd;
System.out.println(res);
}
else if (prvOptrStr.equals("-"))
{
res = fOpnd - sOpnd;
System.out.println(res);
}
}
else
{
prvOpndStr = opndStck.pop();
prvOptrStr = optrStck.pop();
prvPrvOptrStr = optrStck.pop();
sOpnd = Double.parseDouble(curOpndStr);
fOpnd = Double.parseDouble(prvOpndStr);
if (prvOptrStr.equals("*"))
{
res = fOpnd * sOpnd;
System.out.println(res);
}
else if (prvOptrStr.equals("/"))
{
res = fOpnd / sOpnd;
System.out.println(res);
}
}
opndStck.push(res + "");
}
screen.setText(res + "");
}
else if (opndStck.size() <= 1 && optrStck.size() == 1)
{
prvOpndStr = opndStck.pop();
prvOptrStr = optrStck.pop();
}
}
else if (butStr.equals("-"))
{
optrStr = butStr;
ptPshd = false;
if (!optrPshd)
{
if (opndStck.empty() && optrStck.empty())
{
opndStck.push(screen.getText());
optrStck.push(optrStr);
}
else
{
curOpndStr = screen.getText();
curOptrStr = optrStr;
}
optrPshd = true;
}
else
{
optrStck.pop();
optrStck.push(optrStr);
}
}
else if (butStr.equals("*"))
{
optrStr = butStr;
ptPshd = false;
if (!optrPshd)
{
if (opndStck.empty() && optrStck.empty())
{
opndStck.push(screen.getText());
optrStck.push(optrStr);
}
else
{
curOpndStr = screen.getText();
curOptrStr = optrStr;
}
optrPshd = true;
}
else
{
optrStck.pop();
optrStck.push(optrStr);
}
}
else if (butStr.equals("/"))
{
optrStr = butStr;
ptPshd = false;
if (!optrPshd)
{
if (opndStck.empty() && optrStck.empty())
{
opndStck.push(screen.getText());
optrStck.push(optrStr);
}
else
{
curOpndStr = screen.getText();
curOptrStr = optrStr;
}
optrPshd = true;
}
else
{
optrStck.pop();
optrStck.push(optrStr);
}
for (String s : opndStck)
{
System.out.print(s);
}
System.out.println();
for (String s : optrStck)
{
System.out.print(s);
}
System.out.println();
System.out.println();
}
else if (butStr.equals("="))
{
optrStr = butStr;
ptPshd = false;
opndStck.push(screen.getText());
optrStck.push(optrStr);
}
else if (butStr.equals("C"))
{
screen.setText("0");
while (!opndStck.empty())
{
opndStck.pop();
}
while (!optrStck.empty())
{
optrStck.pop();
}
ptPshd = false;
optrPshd = false;
fOpnd = 0;
sOpnd = 0;
res = 0;
exprStr = "";
optrStr = "";
curOpndStr = "";
prvOpndStr = "";
prvPrvOptrStr = "";
curOptrStr = "";
prvOptrStr = "";
}
}
}
ActionListener bl = new ButtonListener();
SingleObjectCalculator()
{
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setSize(250,250);
setVisible(true);
setLayout(new GridBagLayout());
GridBagConstraints gbc = new GridBagConstraints();
Insets bi = new Insets(15, 15, 15, 15);
gbc.gridwidth = 4;
gbc.gridx = 0;
gbc.gridy = 0;
add(screen, gbc);
gbc.gridwidth = 1;
seven = new JButton("7");
gbc.ipady = 5;
gbc.gridx = 0;
gbc.gridy = 1;
add(seven, gbc);
eight = new JButton("8");
//gbc.fill = GridBagConstraints.RELATIVE;
gbc.gridx = 1;
gbc.gridy = 1;
add(eight, gbc);
nine = new JButton("9");
//gbc.fill = GridBagConstraints.RELATIVE;
gbc.gridx = 2;
gbc.gridy = 1;
add(nine, gbc);
plus = new JButton("+");
//gbc.fill = GridBagConstraints.RELATIVE;
gbc.gridx = 3;
gbc.gridy = 1;
add(plus, gbc);
four = new JButton("4");
gbc.weighty = 0;
gbc.gridx = 0;
gbc.gridy = 2;
add(four, gbc);
five = new JButton("5");
//gbc.fill = GridBagConstraints.RELATIVE;
gbc.gridx = 1;
gbc.gridy = 2;
add(five, gbc);
six = new JButton("6");
//gbc.fill = GridBagConstraints.RELATIVE;
gbc.gridx = 2;
gbc.gridy = 2;
add(six, gbc);
minus = new JButton("-");
//gbc.fill = GridBagConstraints.RELATIVE;
gbc.gridx = 3;
gbc.gridy = 2;
add(minus, gbc);
one = new JButton("1");
gbc.weighty = 0;
gbc.gridx = 0;
gbc.gridy = 3;
add(one, gbc);
two = new JButton("2");
//gbc.fill = GridBagConstraints.RELATIVE;
gbc.gridx = 1;
gbc.gridy = 3;
add(two, gbc);
three = new JButton("3");
//gbc.fill = GridBagConstraints.RELATIVE;
gbc.gridx = 2;
gbc.gridy = 3;
add(three, gbc);
times = new JButton("*");
//gbc.fill = GridBagConstraints.RELATIVE;
gbc.gridx = 3;
gbc.gridy = 3;
add(times, gbc);
point = new JButton(".");
gbc.weighty = 0;
gbc.gridx = 0;
gbc.gridy = 4;
add(point, gbc);
zero = new JButton("0");
//gbc.fill = GridBagConstraints.RELATIVE;
gbc.gridx = 1;
gbc.gridy = 4;
add(zero, gbc);
equals = new JButton("=");
//gbc.fill = GridBagConstraints.RELATIVE;
gbc.gridx = 2;
gbc.gridy = 4;
add(equals, gbc);
divide = new JButton("/");
//gbc.fill = GridBagConstraints.RELATIVE;
gbc.gridx = 3;
gbc.gridy = 4;
add(divide, gbc);
clear = new JButton("C");
gbc.gridwidth = 4;
gbc.gridx = 4;
gbc.gridy = 0;
add(clear, gbc);
one.addActionListener(bl);
two.addActionListener(bl);
three.addActionListener(bl);
four.addActionListener(bl);
five.addActionListener(bl);
six.addActionListener(bl);
seven.addActionListener(bl);
eight.addActionListener(bl);
nine.addActionListener(bl);
zero.addActionListener(bl);
point.addActionListener(bl);
equals.addActionListener(bl);
plus.addActionListener(bl);
minus.addActionListener(bl);
times.addActionListener(bl);
divide.addActionListener(bl);
clear.addActionListener(bl);
}
public static void main (String args[])
{
SingleObjectCalculator soc = new SingleObjectCalculator();
}
}
Currently it throws a NumberFormatExcpetion at line 400:
Code java:
sOpnd = Double.parseDouble(curOpndStr);
The JVM claims that it is throwing the exception because the string curOpndStr is empty (as it is when I initialize it at the beginning of actionPerformed()). I am able to trace the error back to a block of code where I think that I reassign curOpndStr a non-empty value.
Code java:
if (opndStck.empty() && optrStck.empty())
{
opndStck.push(screen.getText());
optrStck.push(optrStr);
}
else if (!opndStck.empty() && !optrStck.empty())
{
curOpndStr = screen.getText();
curOptrStr = optrStr;
}
I have test that block of code and know that, when the "+" button is pushed for the first time, opndStck.empty() && optrStck.empty() becomes false, I am confused as to why, when I test the code after it curOpndStr is empty.
Is there some way that I am inadvertantly resetting the value?
I apologize for posting such a long code, but I thought it might help.
Re: Confused about string that I think shouldn't be null
Never mind. I figured it out.
It was silly mistake.
