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Java Scientific calculator GUI

I am working on a calculator with a GUI. I'm not sure how I should gather all the numbers from the user and do the math for them. I tried storing them in variables, but that doesn't really work since I need to be able to have multiple numbers and operators at one time. Any input would be greatly appreciated. Thanks!
import java.util.*;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class GUI extends JFrame implements ActionListener {
private JFrame frame;
private JPanel buttons;
//
private JPanel text;
private JTextField field;
//
private ImageIcon WCU;
private JLabel labelWCU;
///
JButton[] nums = new JButton[10];
JButton[] functions = new JButton[15];
ArrayList<Double> Addition = new ArrayList<>();
double A;
double S;
double M;
double D;
double Answer;
private JButton num1, num2, num3, num4, num5, num6, num7, num8, num9, num0;
private JButton decimal, add, subtract, multiply, divide, equals, squareRoot;
private JButton sin, cos, tan, exclamation, oneOverX, xSquared, log;
private JButton clear;
double input1 = 0, input2 = 0, answer = 0;
char op;
public GUI() {
frame = new JFrame();
buttons = new JPanel();
//
text = new JPanel();
field = new JTextField(30);
//
WCU = new ImageIcon("WCU.png");
labelWCU = new JLabel(WCU);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setTitle("Calculator"); // make sure to center
frame.setSize(525,750);
frame.setLocationRelativeTo(null);
frame.setResizable(false);
frame.setLayout(new BorderLayout());
frame.add(text, BorderLayout.NORTH);
frame.add(buttons, BorderLayout.CENTER);
text.add(field);
field.setEditable(false);
text.setBackground(Color.RED);
buttons.setBackground(Color.red);
buttons.setBorder(BorderFactory.createEmptyBorder(20,50,300,50));
buttons.setLayout(new GridLayout(6,4,20,20));
//
buttons.add(decimal = new JButton ("."));
functions[0] = decimal;
buttons.add(add = new JButton ("+"));
functions[1] = add;
buttons.add(subtract = new JButton ("-"));
functions[2] = subtract;
buttons.add(multiply = new JButton ("*"));
functions[3] = multiply;
buttons.add(divide = new JButton ("/"));
functions[4] = divide;
buttons.add(equals = new JButton ("="));
functions[5] = equals;
buttons.add(squareRoot = new JButton ("√"));
functions[6] = squareRoot;
buttons.add(num1 = new JButton ("1"));
nums[1] = num1;
buttons.add(num2 = new JButton ("2"));
nums[2] = num2;
buttons.add(num3 = new JButton ("3"));
nums[3] = num3;
buttons.add(num4 = new JButton ("4"));
nums[4] = num4;
buttons.add(num5 = new JButton ("5"));
nums[5] = num5;
buttons.add(num6 = new JButton ("6"));
nums[6] = num6;
buttons.add(num7 = new JButton ("7"));
nums[7] = num7;
buttons.add(num8 = new JButton ("8"));
nums[8] = num8;
buttons.add(num9 = new JButton ("9"));
nums[9] = num9;
buttons.add(num0 = new JButton ("0"));
nums[0] = num0;
buttons.add(sin = new JButton ("sin"));
functions[7] = sin;
buttons.add(cos = new JButton ("cos"));
functions[8] = cos;
buttons.add(tan = new JButton ("tan"));
functions[9] = tan;
buttons.add(exclamation = new JButton ("!"));
functions[10] = exclamation;
buttons.add(oneOverX = new JButton ("1/x"));
functions[11] = oneOverX;
buttons.add(xSquared = new JButton ("x^2"));
functions[12] = xSquared;
buttons.add(log = new JButton ("log"));
functions[13] = log;
text.add(clear = new JButton("Clear"));
functions[14] = clear;
labelWCU.setIcon(WCU);
frame.setVisible(true);
//
for (int i = 0; i < 15; i++){
functions[i].addActionListener(this);
functions[i].setFocusable(false);
}
for (int i = 0; i < 10; i++){
nums[i].addActionListener(this);
nums[i].setFocusable(false);
}
}
public void actionPerformed(ActionEvent e){
for (int i = 0; i < 10; i++){
if(e.getSource() == nums[i]){
field.setText(field.getText().concat(String.valueOf(i)));
}
}
if(e.getSource() == decimal){
field.setText(field.getText().concat("."));
}
if(e.getSource() == add){
A = Double.parseDouble(field.getText());
op = '+';
field.setText("");
}
if(e.getSource() == subtract){
input1 = Double.parseDouble(field.getText());
op = '-';
field.setText("");
}
if(e.getSource() == multiply){
input1 = Double.parseDouble(field.getText());
op = '*';
field.setText("");
}
if(e.getSource() == divide){
input1 = Double.parseDouble(field.getText());
op = '/';
field.setText("");
}
if(e.getSource() == equals){
field.setText(String.valueOf(Addition));
}
if(e.getSource() == clear){
field.setText("");
A = 0;
}
}
}

I don't fully understand the purpose of all fields in your class, so I'll propose my own set. If we (ab)use the text field as storage for the current value, two state fields are enough for the basic functionality. It's not necessary to store any more data:
private String firstBinaryOperand = null;
private char binaryOp = ' ';
These fields are used if there is a pending binary operation such as + or -. We don't need them for unary operations. For example, if the user types "700 + 200 =", then
When the "+" button is pressed for the first time, the currently displayed value (700) is stored in firstBinaryOperand and '+' in binaryOp.
When the "=" button is pressed, the current value (200) and the value cached in firstBinaryOperand are added and the result (900) written into the text field.
We therefore need a method that evaluates a pending binary operation if there is one and writes the result into the text field:
// Evaluate pending binary operation, if there is one.
private void evaluateBinaryOp() {
if (binaryOp != ' ') {
double firstOperand = Double.parseDouble(firstBinaryOperand);
double secondOperand = Double.parseDouble(field.getText());
double result;
if (binaryOp == '+') {
field.setText(Double.toString(firstOperand + secondOperand));
} else if (binaryOp == '-') {
field.setText(Double.toString(firstOperand - secondOperand));
}
// Implementation of further binary operands ...
// Update state, there is no longer a pending binary operation
firstBinaryOperand = null;
binaryOp = ' ';
}
}
Addition as an example of a binary operation:
if (e.getSource() == add){
evaluateBinaryOp(); // evaluate pending binary op, if any
firstBinaryOperand = field.getText();
binaryOp = '+';
field.setText("0");
}
Unary operations are simpler, but we still have to check whether there is a pending binary operation and evaluate it first if this is the case:
if (e.getSource() == oneOverX) {
evaluateBinaryOp(); // evaluate pending binary op, if any
double currentValue = Double.parseDouble(field.getText());
field.setText(Double.toString(1.0 / currentValue));
}
All other unary and binary operations can be implemented using the same pattern.
This is going to give you a very basic calculator whose behavior differs a bit from the usual. For example, if the user presses +, they will not see the intermediate result but always 0. The intermediate result isn't lost though as it is stored in the firrstBinaryOperand field in the background. The correct result will be shown once = or another unary operator is used. I hope this answers your question and is enough to get you started, you can then refine the behavior in a second step.

GetChangeGui manual JFrame

I'm trying to write a code for my CS 1 class.
The point of the code is to write a code where you are making change out of a hundred dollar bill out for what ever amount, I need to give back the appropriate bills and coins.
I have to write the JFrame manually
It would be helpful if someone could show me where I'm going wrong in the computation.
/**
*
* #author esamayoa
*/
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class GetChange extends JFrame {
//Declare variables
JButton bCompute, bReset;
JTextField tAmount, tQuarters, tDimes, tNickels, tPennies, tTwenty, tTen, tFive, tOne;
JLabel lAmount, lQuarters, lDimes, lNickels, lPennies, lTwenty, lTen, lFive, lOne;
double amount, diff, totalPaid, quarter, dime, nickel, penny, twenty, ten, five, one;
public GetChange (){
//Set the attributes of the Jframe
setTitle("Eric");
setLocation(500,10);
setSize(450,1000);
setDefaultCloseOperation(EXIT_ON_CLOSE);
setResizable(false);
setVisible(true);
//Create your Gui components
lAmount = new JLabel("Amount");
lQuarters = new JLabel("Quarters:");
lDimes = new JLabel("Dimes:");
lNickels = new JLabel("Nickels:");
lPennies = new JLabel("Pennies:");
lTwenty = new JLabel("Twenties");
lTen = new JLabel("Tens");
lFive = new JLabel("Fives");
lOne = new JLabel("Ones");
tAmount = new JTextField();
tQuarters = new JTextField();
tDimes = new JTextField();
tNickels = new JTextField();
tPennies = new JTextField();
tTwenty = new JTextField();
tTen = new JTextField();
tFive = new JTextField();
tOne = new JTextField();
bReset = new JButton("Reset");
bCompute = new JButton("Compute");
//Add you Gui components to the Jframe
setLayout(new GridLayout(10,2));
add(lAmount);
add(tAmount);
add(lQuarters);
add(tQuarters);
add(lDimes);
add(tDimes);
add(lNickels);
add(tNickels);
add(lPennies);
add(tPennies);
add(lTwenty);
add(tTwenty);
add(lTen);
add(tTen);
add(lFive);
add(tFive);
add(lOne);
add(tOne);
add(bCompute);
add(bReset);
//Updates frame
this.validate();
//Add Action Listeners to buttons
bReset.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent ae) {
tAmount.setText("");
tQuarters.setText("");
tDimes.setText("");
tNickels.setText("");
tPennies.setText("");
tTwenty.setText("");
tTen.setText("");
tFive.setText("");
tOne.setText("");
tAmount.setText("");
}
});
//Create computation for compute button
bCompute.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent ae) {
totalPaid = 100;
amount = Double.parseDouble(tAmount.getText());
diff = totalPaid-amount;
twenty = diff/20;
diff = diff%20;
tTwenty.setText(""+ twenty);
ten = diff/10;
diff = diff%10;
tTen.setText(""+ ten);
five = diff/5;
diff = diff%5;
tFive.setText(""+ five);
one = diff/1;
diff = diff%1;
tOne.setText(""+ one);
quarter = diff/.25;
diff = diff%.25;
tQuarters.setText(""+ quarter);
dime = diff/.1;
diff = diff%.1;
tDimes.setText(""+ dime);
nickel = diff/.05;
diff = diff%.05;
tNickels.setText(""+ nickel);
penny = diff/.01;
diff = diff%.01;
tPennies.setText(""+ penny);
}
});
}
//Main Method
public static void main(String[] args) {
// TODO code application logic here
GetChange myApp = new GetChange();
}
}

To Solve the First problem(Frame not showing) insert the following after all components are added,
this.validate(); // updates frame
To add implementation to the reset button, just use .setText("");
bReset.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent ae) {
tAmount.setText("");
tQuarters.setText("");
tDimes.setText("");
tNickels.setText("");
tPennies.setText("");
tTwenty.setText("");
tTen.setText("");
tFive.setText("");
tOne.setText("");
tResult.setText("");
}
});
To add implementation to the Compute Button...
bCompute.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent ae) {
double Amount = Double.parseDouble(tAmount.getText());
double q = (double) Integer.parseInt(tQuarters.getText()) *.25;
double d = (double) Integer.parseInt(tDimes.getText()) *.10;
double n = (double) Integer.parseInt(tNickels.getText()) *.05;
double p = (double) Integer.parseInt(tPennies.getText()) *.01;
double T = (double) Integer.parseInt(tTwenty.getText()) *20;
double Ten = (double) Integer.parseInt(tTen.getText()) *10;
double Five = (double) Integer.parseInt(tFive.getText()) *5;
double one = (double) Integer.parseInt(tOne.getText()) *1;
double TotalPaid = q+d+n+p+T+Ten+Five+1;
double diff = TotalPaid-Amount;
//Heres an example to create how many twenties you need
int totalTwenties = (int)diff /20;
diff = diff%20;
tTwenty.setText("" + totalTwenties);
}
});
Basically, I got the difference between Amount paid and Amount Cost.
A) Then, the number of times a 20 can fit into the difference is found by /20. Next, I modulus or found the remainder of the difference and twenty.
B) To Find the number of other coins/bills that you need to give as change, repeat the process described in A.

Add values when JCheckBox clicked

My program contains a label with the caption “Choose a coffee” and four check boxes – Americano, Espresso, Double Espresso and Latte. Note: A JCheckBox array is recommended here)
I need to add event handling code to allow the user to purchase one or more items. The bill amount is displayed in a label after the user has made their selections.
The prices are Americano €3.75, Espresso €4.00, Double Espresso €4.50 and Latte €3.50. An array is suitable here also.
As the user makes a choice a label is displayed showing the bill.
I cant figure out how to add the cost when the check box is selected and remove the cost when it is de selected using the arrays.
Any help appreciated.
This is my code so far:
package Lab4EventHandling;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
class Frame3 extends JFrame implements ActionListener {
private Container cPane;
private JLabel tMsg, bMsg;
private JCheckBox americano, espresso, doubleEspresso, latte;
JCheckBox[] boxes = new JCheckBox[]{americano, espresso, doubleEspresso, latte};
private JPanel checkPanel = new JPanel(new GridLayout(0,1));
private Color cl;
private double cost = 0;
private final int WINDOW_WIDTH = 200;
private final int WINDOW_HEIGHT = 200;
private final int x = 550;
private final int y = 400;
public Frame3()
{
cPane = getContentPane();
cl = new Color(150, 150, 250);
cPane.setBackground(cl);
this.setLayout(new BorderLayout(0,1));
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.setLocation(x,y);
this.add(checkPanel, BorderLayout.CENTER);
tMsg = new JLabel("Choose a coffee:" ,SwingConstants.CENTER);
tMsg.setBorder(BorderFactory.createEmptyBorder(4,4,4,4));
this.add(tMsg, BorderLayout.PAGE_START);
americano = new JCheckBox("Americano", false);
checkPanel.add(americano);
americano.addActionListener(this);
espresso = new JCheckBox("Espresso", false);
checkPanel.add(espresso);
espresso.addActionListener(this);
doubleEspresso = new JCheckBox("Double Espresso", false);
checkPanel.add(doubleEspresso);
doubleEspresso.addActionListener(this);
latte = new JCheckBox("Latte", false);
checkPanel.add(latte);
latte.addActionListener(this);
bMsg = new JLabel("Bill is ");
bMsg.setHorizontalAlignment(SwingConstants.CENTER);
bMsg.setBorder(BorderFactory.createEmptyBorder(4,4,4,4));
this.add(bMsg, BorderLayout.SOUTH);
this.setSize(WINDOW_WIDTH, WINDOW_HEIGHT);
this.setVisible(true);
}
public void actionPerformed(ActionEvent e) {
Double[] array = {3.75, 4.00, 4.50, 3.50};
for (JCheckBox box : boxes) {
if(americano.isSelected())
{
cost += 3.75;
String r = String.valueOf(cost);
bMsg.setText(r);
}
if(espresso.isSelected())
{
cost += 4.00;
String r = String.valueOf(cost);
bMsg.setText(r);
}
else if(doubleEspresso.isSelected())
{
cost = 4.50;
String r = String.valueOf(cost);
bMsg.setText(r);
}
else if(latte.isSelected())
{
cost = 3.50;
String r = String.valueOf(cost);
bMsg.setText(r);
}
}
}
public class Frame3Test{
public static void main(String [] args)
{
Frame3 f = new Frame3();
f.setVisible(true);
}
}

Your first problem (which you may or may not have noticed) is your array of JCheckBoxes only contains null elements:
// check boxes are null here
private JCheckBox americano, espresso, doubleEspresso, latte;
// array created with only null elements
JCheckBox[] boxes = new JCheckBox[]{americano, espresso, doubleEspresso, latte};
So you need to create the array after instantiating the actual check boxes.
...
americano = new JCheckBox("Americano", false);
checkPanel.add(americano);
americano.addActionListener(this);
espresso = new JCheckBox("Espresso", false);
checkPanel.add(espresso);
espresso.addActionListener(this);
doubleEspresso = new JCheckBox("Double Espresso", false);
checkPanel.add(doubleEspresso);
doubleEspresso.addActionListener(this);
latte = new JCheckBox("Latte", false);
checkPanel.add(latte);
boxes = new JCheckBox[] {
americano, espresso, doubleEspresso, latte
};
Then the assignment is suggesting to use arrays because you can create another parallel array of prices (which you did). But since you need these prices in parallel you cannot use a for each loop. You need the index. Then you need to recalculate the entire cost every time anything is selected or deselected.
final double[] prices = {
3.75, 4.00, 4.50, 3.50
};
...
double total = 0.0;
for(int i = 0; i < boxes.length; i++) {
if(boxes[i].isSelected()) {
total += prices[i];
}
}
There's two other notes that seem to be outside the scope of the assignment:
You should always make a class for this kind of association.
You should never use double for money. Use BigDecimal or something like it.
Using a class makes logic simpler and not using double makes the calculation not incur error for this decimal addition.
class PricePair {
JCheckBox jCheckBox;
BigDecimal price;
}
BigDecimal total = new BigDecimal("0.00");
for(PricePair option : options) {
if(option.jCheckBox.isSelected()) {
total = total.add(option.price);
}
}

First of all, you're not handling all the checkboxes the same way. For the first two choices, you add the price to the cost:
cost += 3.75;
whereas for the last two choices, you replace the cost:
cost = 4.50;
The first way is the correct way.
Second, there's no reason to have the cost as a field. You should recompute the cost, and it should always start with 0, every time a checkbox selection changes. So cost should be a local variable of the actionPerformed() method.
Third, there's no reason to change the label value before you know the final cost. So the lines
String r = String.valueOf(cost);
bMsg.setText(r);
should only be there once, at the end of the actionPerformed() method, when the final cost is known.
Finally, you want to use it us an array instead of handling each checkbos separately. It's quite easy, you just need to loop over the checkboxes:
double prices = {3.75, 4.00, 4.50, 3.50};
double cost = 0.0;
for (int i = 0; i < boxes.length; i++) {
if (boxes[i].isSelected()) {
double price = prices[i];
cost += price;
}
}
// now display the cost in the label

Although both answers posted here are very helpful I'm adding this one because IMHO arrays are the less Object Oriented thing ever. You can achieve a more robust and OO solution following this hints:
Use
putClientProperty()
method inherited from
JComponent
to hold the prices in the check boxes.
Implement an ActionListener to add/substract the check box price to the total depending on the check box state. Use getClientProperty() method to retrieve the value stored in the check box.
See the example below:
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.math.BigDecimal;
import java.math.BigInteger;
import javax.swing.BoxLayout;
import javax.swing.JCheckBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class Demo {
BigDecimal total = new BigDecimal(BigInteger.ZERO);
private void createAndShowGUI() {
final JLabel totalLabel = new JLabel("Total: ");
ActionListener actionListener = new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
JCheckBox checkBox = (JCheckBox)e.getSource();
BigDecimal value = (BigDecimal)checkBox.getClientProperty("price");
total = checkBox.isSelected() ? total.add(value) : total.subtract(value);
StringBuilder sb = new StringBuilder("Total: ").append(total);
totalLabel.setText(sb.toString());
}
};
JCheckBox americano = new JCheckBox("Americano");
americano.addActionListener(actionListener);
americano.putClientProperty("price", new BigDecimal("3.75"));
JCheckBox espresso = new JCheckBox("Espresso");
espresso.addActionListener(actionListener);
espresso.putClientProperty("price", new BigDecimal("4.00"));
JCheckBox doubleEspresso = new JCheckBox("Double Espresso");
doubleEspresso.addActionListener(actionListener);
doubleEspresso.putClientProperty("price", new BigDecimal("4.50"));
JCheckBox latte = new JCheckBox("Latte");
latte.addActionListener(actionListener);
latte.putClientProperty("price", new BigDecimal("3.50"));
JPanel content = new JPanel();
content.setLayout(new BoxLayout(content, BoxLayout.PAGE_AXIS));
content.add(americano);
content.add(espresso);
content.add(doubleEspresso);
content.add(latte);
content.add(totalLabel);
JFrame frame = new JFrame("Demo");
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
frame.add(content);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
new Demo().createAndShowGUI();
}
});
}
}
This way you can forget about mapping every check box with a value using arrays or maps. If you need to add a new sort of coffee you should simply add 4 lines like this:
JCheckBox newCoffee = new JCheckBox("New Coffee");
newCoffee.addActionListener(actionListener);
newCoffee.putClientProperty("price", new BigDecimal("4.00"));
content.add(newCoffee);

setCharAt a for JLabel

I'm trying to replace setCharAt with something that can be used with a JLabel... I've been on oracle doc's looking for a solution. i don't know if I'm looking for the wrong thing or it just doesn't exists.. if it doesn't exists how could i work around that? i understand my naming convention is off and will be changing them as soon as possible...
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import javax.swing.*;
public class HangmanPanel extends JPanel {
static Boolean FOUND;
private static final long serialVersionUID = -5793357804828609325L;
public static String answerKey() {
//get random array element
String array[] = new String[10];
array[0] = "hamlet";
array[1] = "mysts of avalon";
array[2] = "the iliad";
array[3] = "tales from edger allan poe";
array[4] = "the children of hurin";
array[5] = "the red b" +
"+adge of courage";
array[6] = "of mice and men";
array[7] = "utopia";
array[8] = "chariots of the gods";
array[9] = "a brief history of time";
ArrayList<String> list = new ArrayList<String>(Arrays.asList(array));
Collections.shuffle(list);
String s = list.get(0);
return s;
}
public StringBuilder dashReplace(String s) {
//replace non-white space char with dashes and creates StringBuilder Object
String tW = s.replaceAll("\\S", "-");
System.out.print(tW + "\n");
StringBuilder AnswerKey = new StringBuilder(tW);
return AnswerKey;
}
public static int findAndReplace(String s, JLabel answerKey, String sc,
char ch) {
//find position of user input and replace
int pos = -1;
FOUND = false;
while(true){
pos = s.indexOf(sc, pos+1);
if(pos < 0){
break;
}else{
FOUND = true;
//setCharAt dosen't work for JLable
answerKey.setCharAt(pos, ch);
}
}
JLabel AnswerKey2 = new JLabel(answerKey.toString());
return pos;
}
public HangmanPanel(final String s){
this.setLayout(null);
JLabel heading = new JLabel("Welcome to the Hangman App");
JButton Button = new JButton("Ok");
//get input
JLabel tfLable = new JLabel("Please Enter a Letter:");
final JLabel AnswerKey = new JLabel(dashReplace(answerKey()).toString());
final JTextField text = new JTextField(10);
heading.setSize(200, 50);
tfLable.setSize(150, 50);
text.setSize(50, 30);
Button.setSize(60, 20);
AnswerKey.setSize(200, 100);
heading.setLocation(300, 10);
tfLable.setLocation(50, 40);
text.setLocation(50, 80);
Button.setLocation(100, 85);
AnswerKey.setLocation(100,85);
this.add(heading);
this.add(tfLable);
this.add(text);
this.add(Button);
this.add(AnswerKey);
Button.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
// can't access text
String sc = text.getText();
char ch = sc.charAt(0);
findAndReplace(s, AnswerKey, sc, ch);
}
});
}
}

Why are you trying to use setCharAt(...) with a JLabel. A label is meant to display static text. The only way to change it is to replace the entire string.
I guess you could do something like:
StringBuilder text = label.getText();
text.setCharAt(...);
label.setText( text.toString() );
Another option would be to use a JTextField that looks like a JLabel:
JTextField label = new JTextField(...);
label.setEditable(false);
label.setBorder(null);
label.setOpaque(false);
Then when you need to change the text you could do:
label.select(...);
label.replaceSelection(...);

The only method available for setting text for JLabel components is setText. Also Strings are immutable. Therefore, you can use StringBuilder:
StringBuilder builder = new StringBuilder(answerKey.getText());
builder.setCharAt(pos, ch);
answerKey.setText(builder.toString());

Retrieving a double from a JTextArea while solving for X

Ok, I'm kinda new to java. I'm making a program that solves for one step equations. I'm having some difficulties running it though. Here is the code for my main file, Main.java:
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class Main extends JFrame implements ActionListener {
private static final long serialVersionUID = 1L;
Solve solve = new Solve();
JButton add = new JButton("Add");
JButton sub = new JButton("Subtract");
JButton mult = new JButton("Multiply");
JButton div = new JButton("Divide");
JButton solv = new JButton("Solve!");
JTextArea one = new JTextArea();
JLabel two = new JLabel(" = ");
JLabel three = new JLabel("X");
JLabel four = new JLabel();
JTextArea five = new JTextArea();
JLabel solved = new JLabel();
JPanel row1 = new JPanel();
JPanel row2 = new JPanel();
JPanel row3 = new JPanel();
public double funct;
public Main() {
super("Solving a one step equation!");
setSize(500, 500);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setVisible(true);
GridLayout layout = new GridLayout();
setLayout(layout);
FlowLayout layout1 = new FlowLayout(FlowLayout.CENTER);
row1.setLayout(layout1);
row1.add(add);
row1.add(sub);
row1.add(mult);
row1.add(div);
row1.add(solv);
add(row1);
add.addActionListener(this);
sub.addActionListener(this);
mult.addActionListener(this);
div.addActionListener(this);
solv.addActionListener(this);
GridLayout layout2 = new GridLayout(1, 1, 1, 1);
row2.setLayout(layout2);
row2.add(one, BorderLayout.CENTER);
row2.add(two, BorderLayout.CENTER);
row2.add(three, BorderLayout.CENTER);
row2.add(four, BorderLayout.CENTER);
row2.add(five);
add(row2, BorderLayout.CENTER);
GridLayout layout3 = new GridLayout(5, 5, 5, 5);
row3.setLayout(layout3);
row3.add(solved);
add(row3);
}
public static void main(String[] args) {
Main frame = new Main();
}
public void actionPerformed(ActionEvent evt) {
Object source = evt.getSource();
if(source == add)
{
four.setText(" + ");
funct = 1;
}
else if(source == sub)
{
four.setText(" - ");
funct = 2;
}
else if(source == mult)
{
four.setText(" * ");
funct = 3;
}
else if(source == div)
{
four.setText(" / ");
funct = 4;
}
if(source == solv)
{
if(funct == 1)
{
double Ones = Double.parseDouble(three.getText());
double Twos = Double.parseDouble(three.getText());
solved.setText("X = " + solve.Add(Ones, Twos));
}
else if(funct == 2)
{
double Ones = Double.parseDouble(three.getText());
double Twos = Double.parseDouble(three.getText());
solved.setText("X = " + solve.Sub(Ones, Twos));
}
else if(funct == 3)
{
double Ones = Double.parseDouble(three.getText());
double Twos = Double.parseDouble(three.getText());
solved.setText("X = " + solve.Mult(Ones, Twos));
}
else if(funct == 4)
{
double Ones = Double.parseDouble(three.getText());
double Twos = Double.parseDouble(three.getText());
solved.setText("X = " + solve.Div(Ones, Twos));
}
}
}
}
Here is the code for my other file, Solve.java
public class Solve {
public double Add(double One, double Two)
{
return One - Two;
}
public double Sub(double One, double Two)
{
return One + Two;
}
public double Mult(double One, double Two)
{
return One / Two;
}
public double Div(double One, double Two)
{
return One * Two;
}
}
Some help would be appreciated. Anyone see what I'm doing wrong?

You get a NumberFormatException once 'Solve' button is clicked. It seems like a copy/paste issue - you are not retrieving the correct numbers. You are trying to convert 'X' string to double. It is best if you give meaningful names to your variables. To fix the exception, try this, replace :
double Ones = Double.parseDouble(three.getText());
double Twos = Double.parseDouble(three.getText());
with:
double Ones = Double.parseDouble(one.getText());
double Twos = Double.parseDouble(five.getText());
Get familiar with Java Code Conventions, Naming Conventions section in particular.

In addition to #Max's helpful answer, here are a few other suggestions:
Setting the frame's layout to new GridLayout() defaults to a single row and column with no padding. As an alternative, consider new GridLayout(0, 1, 5, 5), which produces any number of rows in one column with 5x5 padding. Then you can focus on the layout of each row:
row1.setLayout(new FlowLayout(FlowLayout.CENTER));
row2.setLayout(new FlowLayout(FlowLayout.CENTER));
row3.setLayout(new GridLayout(1, 1, 5, 5));
Move your setVisible() call to the end of the frame's constructor:
pack();
setLocationRelativeTo(null);
setVisible(true);
Consider getRootPane().setDefaultButton(solv) to make the Solve button the default.
Consider making addition the default:
private JLabel four = new JLabel("+");
private int funct = 1; // add by default
Consider using JTextField for number entry:
private JTextField one = new JTextField(10);
private JTextField five = new JTextField(10);