Develop Reference

Binary to Decimal Converter GUI JAVA

I've tried to finish my program but it cannot convert to binary what do you think is the problem? if I press convert it would simple run a script saying, string index is out of range on how many digits of the binary. and if so how would I improve the codes. Thank you for the ones who would comment to this thread :>
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
public class BinaryGUI extends BinaryGUIDemo {
public static void main(String[] args) {
new BinaryGUI();
}
private JFrame frame;
private JButton button;
private JTextField text;
private JTextField text2;
private String decimalnumber = null;
public BinaryGUI() {
frame = new JFrame("Conversion!");
JLabel label = new JLabel("Binary:");
frame.setLayout(new FlowLayout());
frame.add(label);
text = new JTextField(15);
frame.add(text);
JLabel label2 = new JLabel("Decimal:");
frame.add(label2);
text2 = new JTextField(15);
frame.add(text2);
button = new JButton("Convert");
button.addActionListener(new ButtonListener());
frame.add(button);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(250, 300);
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public void Convert() {
String binary = text.getText();
int i;
for (i = 0; i < binary.length(); i++) {
char select = binary.charAt(binary.length() - i);
char number = (char) (select * Math.pow(2, i));
decimalnumber += number;
}
}
public class ButtonListener implements ActionListener {
public void actionPerformed(ActionEvent e) {
Convert();
if (button.getText().equals("Convert")) {
text2.setText(decimalnumber);
text.getText();
text2.getText();
} else {
}
}
}
}

There are a couple of issues with your code:
Index ouf of bounds
When using str.charAt() you can only have indices between 0 inclusive and str.length - 1 inclusive, meaning that str.charAt(str.length) will result in an out of bounds error. To prevent that use binary.length() - i - 1 instead of binary.length() - i.
Type-casting to char
What you do in this line char number = (char) (select * Math.pow(2, i)); doesn't make any sense. You want to have an int returned not a char. select is a char here and doesn't hold the value 0 or 1 as you seem to think it does. Also Math.pow() is unnecessary here, you can just use a bit-shift which will be faster and prevent unnecessary type casts.
Ignore 0 bits
As I've pointed out before select hold the chars '0' and '1' which don't translate to 0 and 1 integers as you seem to think. Therefore your calculation with select * Math.pow(2, i) yields unexpected results. Instead you could just use an if condition checking whether a char is '0'. This way you also save an expensive multiplication operation.
As you only index the individual chars of the String you could just transform everything to a char array.
Here an implementation showing how to convert from a binary string to a decimal number. It also shows how you can use Integer::toBinaryString() to convert in the opposite direction.
public class Application {
public static void main(String[] args) {
System.out.println(convBinaryStringToInt("1001"));
System.out.println(convBinaryStringToInt("0001"));
System.out.println(convBinaryStringToInt("0010"));
System.out.println(convBinaryStringToInt("0011"));
// convert the other way round
System.out.println(Integer.toBinaryString(9));
System.out.println(Integer.toBinaryString(1));
System.out.println(Integer.toBinaryString(2));
System.out.println(Integer.toBinaryString(3));
}
public static int convBinaryStringToInt(String binary) {
int decimalNumber = 0;
var bits = binary.toCharArray();
for (int i = 0; i < bits.length; i++) {
// add -1 otherwise you will run out of bounds
char bit = bits[bits.length - i - 1];
// skip zeros
if(bit == '0') continue;
// now we know we have a one bit, instead of using Math.pow() we can just bit shift which is faster and
// prevents unnecessary type casting
// shift 1 bit to left
int number = 1 << i;
decimalNumber += number;
}
return decimalNumber;
}
}
Expected output:
9
1
2
3
1001
1
10
11

CODE FOR CONVERTING
this is what I used in converting binary to decimal. but instead of getting decimal it prints out null+decimal and the maximum binary numbers that it could read is 2 binary number example: Binary:111 when converted to decimal it prints out Null24 which is 11000 in binary that's the problem. When getting big binary numbers 8 digits it explodes and I dont know how to fix this.
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
public class BinaryGUI extends BinaryGUIDemo {
public static void main(String[] args) {
new BinaryGUI();
int n;
String numInput;
String binary;
numInput = JOptionPane.showInputDialog(null, "Enter a number:");
n = Integer.parseInt(numInput);
binary = Integer.toBinaryString(n);
JOptionPane.showMessageDialog(null, "Binary equivalent is: " +binary);
}
private JFrame frame;
private JButton button;
private JTextField text;
private JTextField text2;
private String decimalnumber = null;
public BinaryGUI() {
frame = new JFrame("Conversion!");
JLabel label = new JLabel("Binary:");
frame.setLayout(new FlowLayout());
frame.add(label);
text = new JTextField(15);
frame.add(text);
JLabel label2 = new JLabel("Decimal:");
frame.add(label2);
text2 = new JTextField(15);
frame.add(text2);
button = new JButton("Convert");
button.addActionListener(new ButtonListener());
frame.add(button);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(250, 300);
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public void Convert() {
String binary = text.getText();
var bits = binary.toCharArray();
for (int i = 1; i < bits.length; i++) {
char select = binary.charAt(binary.length() - i - 1);
if(select == '0') continue;
int number = 1 << i;
decimalnumber += number;
}
}
public class ButtonListener implements ActionListener {
public void actionPerformed(ActionEvent e) {
Convert();
if (button.getText().equals("Convert")) {
text2.setText(decimalnumber);
text.getText();
text2.getText();
} else {
}
}
}
}

Custom java calculator troubleshooting

New programmer here, I have been working for a few days on this bit of code that is meant to create a UI where I input a basement's perimeter length (textfield integer), if a new pump is needed (combobox string), if there is an outlet nearby (combobox string), and how many hours It will take to prepare a site (textfield integer), and I calculate my costs to complete a job. I was able to set up a UI where I can enter the inputs and press a button to calculate but I'm having trouble connecting the button I made to the formula I made to generate a price. Here is my code:
package packagepackage;
import packagepackage.HintTextFieldUI;
import java.awt.*;
import java.awt.BorderLayout;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class CP_GUI implements ActionListener {
String[] sumpo = {"New sump pump","Existing sump pump"};
String[] electo = {"There is an outlet within 6 feet of sump pump","There is no outlet nearby, or I do not need a new one"};
Integer estimatex = 0;
String esto = String.valueOf(estimatex);
public volatile String estimatoof = "Estimated Cost: ${}".format(esto);
private JComboBox sump = new JComboBox(sumpo);
private JComboBox elec = new JComboBox(electo);
private JTextField linear = new JTextField();
private JTextField prep = new JTextField();
private JLabel title = new JLabel("Drain Tile Calculator");
private JButton calculate = new JButton("Calculate!");
public JLabel estimate = new JLabel(estimatoof);
private JFrame frame = new JFrame();
private JPanel panel = new JPanel();
public CP_GUI() {
linear.addActionListener(this);
calculate.addActionListener(this);
elec.addActionListener(this);
sump.addActionListener(this);
prep.addActionListener(this);
// the panel with the button and text
JPanel panel = new JPanel();
panel.setBorder(BorderFactory.createEmptyBorder(400, 400, 100, 100));
panel.setLayout(new GridLayout(0, 1));
panel.add(linear);
panel.add(sump);
panel.add(elec);
panel.add(prep);
frame.add(panel, BorderLayout.CENTER);
panel.add(title);
calculate.addActionListener(this);
panel.add(calculate);
// set up the frame and display it
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setTitle("Drain Tile Calculator");
frame.pack();
frame.setVisible(true);
linear.setUI(new HintTextFieldUI("Perimeter length", true));
prep.setUI(new HintTextFieldUI("Hours of preptime", true));}
// create one Frame
public static void main(String[] args) {
new CP_GUI();
}
#Override
public void actionPerformed(ActionEvent e){
// TODO Auto-generated method stub
if(e.getSource()==linear) {String input = linear.getText();
Integer pars = Integer.parseInt(input);
Integer distVar = pars *= 13;
estimatex += distVar;
} else if (e.getSource()==sump) {String inputa = sump.getToolTipText();
int sumpa = 0;
if(inputa == "New sump pump" | inputa == "yes") {
sumpa += 260;}
estimatex += sumpa;
} else if (e.getSource()==elec) {String inputb =elec.getToolTipText();
int eleca = 0;
if("There is an outlet within 6 feet of the sump pump".equals(inputb)) {
eleca += 1;
}
eleca *= 280;
estimatex += eleca;
}
else if (e.getSource()==prep) {String inputc = prep.getText();
int parsa = Integer.parseInt(inputc);
int prepCost = parsa += 1;
prepCost *= 110;
estimatex += prepCost;
} else if (e.getSource()==linear) {
String disto = linear.getText();
int di = Integer.parseInt(disto);
di *= 13;
String pumpo = (String)sump.getSelectedItem();
int sumpo = 0;
if ("New sump pump".equals(pumpo)) {
sumpo += 260;
}
String ele = (String)elec.getSelectedItem();
int elc = Integer.parseInt(ele);
elc *= 280;
String clea = prep.getText();
int cla = Integer.parseInt(clea);
cla += 1;
cla *= 110;
int cali = 0;
cali += di;
cali += sumpo;
cali += elc;
cali += cla;
estimatex = cali;
}
}
}
Edit: Made the suggested edits made so far and now the UI opens and works, the only issue is that the estimated price does not show up. Am I connecting the action listener correctly?

Your "primary" problem is right here...
String disto = String.valueOf(linear);
where linear is a JTextField, so the above call will generate something like...
javax.swing.JTextField[,0,0,0x0,invalid,layout=javax.swing.plaf.basic.BasicTextUI$UpdateHandler,alignmentX=0.0,alignmentY=0.0,border=com.apple.laf.AquaTextFieldBorder#4e323305,flags=288,maximumSize=,minimumSize=,preferredSize=,caretColor=javax.swing.plaf.ColorUIResource[r=0,g=0,b=0],disabledTextColor=javax.swing.plaf.ColorUIResource[r=128,g=128,b=128],editable=true,margin=javax.swing.plaf.InsetsUIResource[top=0,left=0,bottom=0,right=0],selectedTextColor=com.apple.laf.AquaImageFactory$SystemColorProxy[r=0,g=0,b=0],selectionColor=com.apple.laf.AquaImageFactory$SystemColorProxy[r=165,g=205,b=255],columns=0,columnWidth=0,command=,horizontalAlignment=LEADING]
which is obviously not what you're looking for.
You should probably be just doing something like...
String disto = linear.getText();
pumpo == "New sump pump" is also not how you compare a String in Java, you should be using "New sump pump".equals(pumpo) ... but I suspect you're going to have the same issues as mentioned above.
I really recommend you take the time to read through Creating a GUI With Swing as well as taking the time to come to grips with the core basics of the language

Image keeps on repeating although it is already randomized

I'm developing a simple game where all the images are randomized. I've noticed that some of the image are repeated although I have put the random code. I'm still new to Java. I hope that someone can help me solve my problem. Below is my coding.
import java.awt.*;
import java.awt.event.*;
import java.sql.*;
import java.util.Random;
import javax.swing.*;
public class Task1 extends JFrame implements KeyListener,ActionListener {
JFrame frame = new JFrame("FYP");
JTextField textField = new JTextField();
JButton btnNext = new JButton("NEXT");
int sum=0;
int Error=0;int total_test = 0;
static String inputID;
static int index;
String[] imgFileHP = {"1.jpg","3.jpg","4.jpg","7.jpg","9.jpg","10.jpg","12.jpg","16.jpg","17.jpg","18.jpg"};
String[] imgNo = {"5","4","6","3","5","3","4","4","6","6"};
int randomNo;
Random rand = new Random();
public Task1(String inputID)
{
frame.setSize(2200,2500);
frame.setLocationRelativeTo(null);
frame.setVisible(true);
frame.getContentPane().setLayout(new BorderLayout(0, 0));
Task(inputID);
}
public void Task(String inputID)
{
JPanel panel = new JPanel();
JLabel labelUsername = new JLabel("");
frame.getContentPane().add(panel, BorderLayout.CENTER);
panel.setBackground(Color.WHITE);
Collections.shuffle(Arrays.asList(imgFileHP));
Set<Integer> uniqueList = new HashSet<Integer>();//This would create list with the number 0 to 9
for(int count=0;count<imgFileHP.length;count++){
uniqueList.add(count);
labelUsername.setIcon(new ImageIcon(getClass().getResource("/image/" + imgFileHP[count])));
if(!uniqueList.isEmpty()){
index = (int) (Math.random() * (upper - lower)) + lower;
if(uniqueList.contains(index)){
uniqueList.remove(index);//particular number is delete from the list so that duplicate images doesnt show up
System.out.println(imgFileHP[r]);//This printf statement is just for your reference
}
}
}
textField.setText("");
textField.setColumns(10);
textField.addKeyListener(this);
btnNext.addActionListener(this);
panel.add(labelUsername);
panel.add(textField);
panel.add(btnNext);
frame.setVisible(true);
}
public void actionPerformed(ActionEvent ae)
{
if(!textField.getText().equals("")){
total_test += 1;
if(isNumeric(textField.getText())){
//********************Correct Integer**********************
if(Integer.valueOf(imgNo[randomNo])==Integer.valueOf(textField.getText())){
//********************Correct Answer**********************
System.out.println("Correct");
sum+=1;
}else{
//********************Incorrect Answer**********************
System.out.println("Incorrect");
Error+=1;
}
refreshFrame();
}else{
//********************Incorrect Integer/Alphabet**********************
System.out.println("Invalid");
Error+=1;
refreshFrame();
}
}else{
System.out.println("Null Input");
}
//System.out.println(Integer.valueOf(imgNo[randomNo]));
}
public void refreshFrame(){
if(total_test>=10){
// add result page to see how many score
//Task2(sum, Error);
System.out.println("Correct: "+sum+" Incorrect: "+Error);
frame.dispose();
}else{
btnNext.removeActionListener(this);
frame.getContentPane().removeAll();
getContentPane().removeAll();
Task(inputID);
}
}
public static void main(String args[]) {
Task1 a = new Task1(inputID);
}
#Override
public void keyPressed(KeyEvent e) {
// TODO Auto-generated method stub
}
#Override
public void keyReleased(KeyEvent e) {
// TODO Auto-generated method stub
}
#Override
public void keyTyped(KeyEvent e) {
// TODO Auto-generated method stub
}
public static boolean isNumeric(String str)
{
try
{
Integer.valueOf(str);
}
catch(NumberFormatException nfe)
{
return false;
}
return true;
}
}
EDIT part (But some of the image is still repeating.)
Collections.shuffle(Arrays.asList(imgFileHP));
Set<Integer> uniqueList = new HashSet<Integer>();//This would create list with the number 0 to 9
for(int count=0;count<imgFileHP.length;count++){
uniqueList.add(count);
}
if(!uniqueList.isEmpty()){
index = (int) (Math.random() * (upper - lower)) + lower;
randomNo = index;
if(uniqueList.contains(index)){
labelUsername.setIcon(new ImageIcon(getClass().getResource("/image/" + imgFileHP[index])));
uniqueList.remove(index);//particular number is delete from the list so that duplicate images doesnt show up
System.out.println(imgFileHP[r]);//This printf statement is just for your reference
}
}

Here is how Random works. Even though you have mentioned rand.nextInt(10);but everytime it gets called, there is not pre-defined rule in java that it has to generate unique numbers and not the duplicate the previously generated ones.
For Example:
when you call -
int index = rand.nextInt(10); // Index could be 2
index = rand.nextInt(10); // Now again the value could be 2 as well
So what you need to do is you have to add an extra piece of code to check the uniqueness every time random is called.
Since you want to generate numbers between 0 to 10. Try the following code, it might help you understand.
String[] imgFileHP = {"1.jpg","3.jpg","4.jpg","7.jpg","9.jpg","10.jpg","12.jpg","16.jpg","17.jpg","18.jpg"};
int upper = imgFileHP.length;
int lower = 0;
int r=0;
int index=0;
Set<Integer> uniqueList = new HashSet<Integer>();//This would create list with the number 0 to 9
for(int count=0;count<imgFileHP.length;count++){
uniqueList.add(count);
}
if(!uniqueList.isEmpty()){
index = (int) (Math.random() * (upper - lower)) + lower;
if(uniqueList.contains(index)){
uniqueList.remove(index);//particular number is delete from the list so that duplicate images doesnt show up
System.out.println(imgFileHP[r]);//This printf statement is just for your reference
}
}
Another easier method is to use Collections.Shuffle as shown below:
Collections.shuffle(Arrays.asList(imgFileHP));
Example of Collection.shuffle().
Lets say you have an array String[] arr = {"abc","def","xyz","bla"}
when you do Collections.shuffle(Arrays.asList(arr));
then print array from index 0 to 3. Array might be shuffled something like this: {"def","bla","abc","xyz"}
**EDIT 2:**Solution based on your edit in main code:
for(int count=0;count<imgFileHP.length;count++){//first add the counters into List
uniqueList.add(count);
}
if(!uniqueList.isEmpty()){
index = (int) (Math.random() * (upper - lower)) + lower;
if(uniqueList.contains(index)){
labelUsername.setIcon(new ImageIcon(getClass().getResource("/image/" + imgFileHP[index])));
uniqueList.remove(index);//particular number is delete from the list so that duplicate images doesnt show up
System.out.println(imgFileHP[r]);//This printf statement is just for your reference
}
}

How to fill JComboBox after user fills necessary text fields?

I want to add a JComboBox to my main panel and fill it with an ArrayList I made in a different method named rectSizeList (which right now prints the ArrayList to the console), this method gets its parameters from another static method named actionPerformed. I cant figure a way to take the filled array after user input to fill my ComboBox. Any help will be appreciated.
All comment is this format are to aid question:
/*
* Like so
*
*/
All other comments are to help whomever my want to compile and run, so that they might understand what is going on.
Main class
import javax.swing.*;
public class ductulatorApp
{
public static void main(String[] args)
{
JFrame frame = new DuctulatorFrame();
frame.setVisible(true);
}
}
Frame class
import javax.swing.*;
import java.awt.*;
public class DuctulatorFrame extends JFrame
{
private static final long serialVersionUID = 1L;
public DuctulatorFrame()
{
setTitle("Test Scores");
setSize(267, 200);
centerWindow(this);
setResizable(false);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JPanel panel = new DuctulatorPanel();
this.add(panel);
}
private void centerWindow(Window w)
{
Toolkit tk = Toolkit.getDefaultToolkit();
Dimension d = tk.getScreenSize();
setLocation((d.width-w.getWidth())/2, (d.height-w.getHeight())/2);
}
}
Panel class
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.text.*;
import java.util.ArrayList;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
public class DuctulatorPanel extends JPanel implements ActionListener
{
private static final long serialVersionUID = 1L;
private JTextField staticTextField,
cfmTextField,
rductTextField,
sqductTextField;
private JLabel staticLabel,
cfmLabel,
rductLabel,
sqductLabel;
private JButton calculateButton,
exitButton,
clearButton;
private JComboBox ductSizes; //JComboBox instance
private String[] ductList; //Array to fill JComboBox
double staticP; //static pressure entered by user
double cfm; //cfm entered by user
double deSQ;
double de; //round duct diameter
double pi = 3.14;
double ca; //round duct surface area
double radious;
double sqrA; //rectangular duct area
//two sides of rectangular duct
double a = 4;
double b = 4;
String squareduct;
public DuctulatorPanel()
{
// Creates main panel for labels and text fields
JPanel displayPanel = new JPanel();
displayPanel.setLayout(new FlowLayout(FlowLayout.RIGHT));
staticLabel = new JLabel("Static pressure:");
displayPanel.add(staticLabel);
staticTextField = new JTextField(10);
displayPanel.add(staticTextField);
cfmLabel = new JLabel(" CFM:");
displayPanel.add(cfmLabel);
cfmTextField = new JTextField(10);
displayPanel.add(cfmTextField);
rductLabel = new JLabel("Round Duct:");
displayPanel.add(rductLabel);
rductTextField = new JTextField(15);
rductTextField.setEditable(false);
rductTextField.setFocusable(false);
displayPanel.add(rductTextField);
sqductLabel = new JLabel("Square Duct:");
displayPanel.add(sqductLabel);
/*
* This is where I want to add my JComboBox problem is I want to populate ductList arr
* with the array inside rectSizeList(int number) BELOW
* right now this method only prints my array to the console
* this method takes its parameters from the value assigned to
* actionperformed(ActionEvent e)
* below is comboBox commented out
*/
//ductList = new String[list.size]; THIS IS ASSUMING I COULD SOME HOW TRANSFER
//ductList = list.toArray(ductList); ARRAYLIST UP HERE AND NAME IT LIST AND USE IT
//ductSizes = new JComboBox(ductList);
//ductSizes.setSelectedIndex(1);
//displayPanel.add(ductSizes);
sqductTextField = new JTextField(10);
sqductTextField.setEditable(false);
sqductTextField.setFocusable(false);
displayPanel.add(sqductTextField);
JPanel buttonPanel = new JPanel();
buttonPanel.setLayout(new FlowLayout(FlowLayout.RIGHT));
calculateButton = new JButton("Calculate");
calculateButton.addActionListener(this);
buttonPanel.add(calculateButton);
clearButton = new JButton("Clear");
clearButton.addActionListener(this);
buttonPanel.add(clearButton);
exitButton = new JButton("Exit");
exitButton.addActionListener(this);
buttonPanel.add(exitButton);
this.setLayout(new BorderLayout());
this.add(displayPanel, BorderLayout.CENTER);
this.add(buttonPanel, BorderLayout.SOUTH);
}
public void actionPerformed(ActionEvent e)
{
NumberFormat number = NumberFormat.getNumberInstance();
number.setMaximumFractionDigits(1);
Object source = e.getSource();
if(source == exitButton)System.exit(0);
else if(source == clearButton)
{
staticTextField.setText("");
cfmTextField.setText("");
rductTextField.setText("");
sqductTextField.setText("");
staticP = 0;
cfm = 0;
deSQ = 0;
}
else if(source == calculateButton)
{
try
{
staticP = Double.parseDouble(staticTextField.getText());
cfm = Double.parseDouble(cfmTextField.getText());
}
catch(NumberFormatException nfe)
{
staticTextField.setText("Invalid input");
staticP = 0;
cfm = 0;
deSQ = 0;
de = 0;
}
deSQ = staticP * (0.109136 * Math.pow(cfm, 1.9)); //Calculate round duct
de = Math.pow(deSQ, 0.199) * 2.5; //diameter
// Calculate round duct surface area
radious = de/2;
ca = (radious * radious) * pi;
ca = (int)ca;
rectSizeList((int)ca);
double i = 0;
for(i=0; i<ca; i++)
{
a = a + 0.5;
b = b + 0.5;
i = a * b; // convert round duct to rectangular duct
}
sqrA = i;
a = (int)a;
b = (int)b;
rductTextField.setText(number.format(de));
squareduct = (a + " x " + b);
sqductTextField.setText(squareduct);
}
}
public ArrayList<String> rectSizeList(int number)
{
if (number <= 0) throw new IllegalArgumentException("The number should be greater than 0.");
int i = 0;
int j = 0;
/*
* This is the array list I am hoping to use in order to fill array for
* comboBox
*/
ArrayList<String> rectangularDucts = new ArrayList<String>(); //Create array for rectangular duct
// Fill array for rectangular duct using nested for loop
/*
* If statement will ensure the result is with in range of surface
* area of duct
*/
for(i=4; i<=50; i++)
{
for(j=4; j<=50; j++)
{
if(number == i*j || (i*j)+1 == number || (i*j)-2 == number)
{
rectangularDucts.add(i + " x " + j);
}
}
if(number == i*j || (i*j)+1 == number || (i*j)-2 == number)
{
rectangularDucts.add(i + " x " + j);
}
}
System.out.println(rectangularDucts);
return rectangularDucts;
}
}

I think that your problem is easily solved with just a DefaultComboBoxModel object, or in your situation (I guess), a DefaultComboBoxModel<String> object. Give your class this field, create your JComboBox with this as its model, by passing it into the constructor, and then fill this model object as the need arises.
For example:
import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;
import javax.swing.*;
public class ComboModelEg extends JPanel {
private DefaultComboBoxModel<String> comboModel = new DefaultComboBoxModel<>();
private JComboBox<String> comboBox = new JComboBox<>(comboModel);
private JTextField textField = new JTextField(5);
public ComboModelEg() {
// so combo box is wide enough
comboBox.setPrototypeDisplayValue(" ");
add(comboBox);
add(textField);
add(new JButton(new AddToComboAction("Add Text", KeyEvent.VK_A)));
}
// AbstractAction is like a *super* ActionListener
private class AddToComboAction extends AbstractAction {
public AddToComboAction(String name, int mnemonic) {
super(name); // button's text
putValue(MNEMONIC_KEY, mnemonic); // button's mnemonic key
}
#Override
public void actionPerformed(ActionEvent e) {
String text = textField.getText(); //get text from text field
comboModel.addElement(text); // and put it into combo box's model
}
}
private static void createAndShowGui() {
ComboModelEg mainPanel = new ComboModelEg();
JFrame frame = new JFrame("ComboModelEg");
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
frame.getContentPane().add(mainPanel);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}
Translated to your code, it could look something like:
for (i = 4; i <= 50; i++) {
for (j = 4; j <= 50; j++) {
if (number == i * j || (i * j) + 1 == number
|| (i * j) - 2 == number) {
// rectangularDucts.add(i + " x " + j); //!!
comboModel.addElement(i + " x " + j); //!!
}
}
if (number == i * j || (i * j) + 1 == number || (i * j) - 2 == number) {
// rectangularDucts.add(i + " x " + j);
comboModel.addElement(i + " x " + j); //!!
}
}

this is how i do it
ArrayList<String> myList = new ArrayList<>();
//some code to populate the list
jComboBox.removeAllItems();
for(int i=0;i<myList.size();i++){
jComboBox.addItem(myList.get(i));
}

Java Scroll bar

I want to add scroll bar to my text area so that if the user inputs a number greater than 20 the text are should have a scroll bar.
Basically I am trying to make a application where user inputs a number he wants the multiplication table and also he inputs up to what number he wants the table to be displayed.But my application show table up to 20 e.g 12 X 20 = 240. and the rest is hidden.
public class LayoutM extends JFrame implements ActionListener {
private JTextField num1;
private JTextField num2;
private JTextArea answer;
private JButton go;
private int num11;
private int num22;
public LayoutM(){
super("Multiplication");
setLayout(new FlowLayout());
Dimension numDim = new Dimension(60,20);
Dimension ansDim = new Dimension(200,300);
Dimension goDim = new Dimension(60,20);
num1 = new JTextField("Number");
num1.setPreferredSize(numDim);
num2 = new JTextField("Upto");
num2.setPreferredSize(numDim);
go = new JButton("GO");
num2.setPreferredSize(goDim);
answer = new JTextArea(20,20);
answer.setPreferredSize(ansDim);
answer.setEditable(false);
add(num1, BorderLayout.CENTER);
add(num2,BorderLayout.CENTER);
add(go,BorderLayout.CENTER);
add(answer,BorderLayout.SOUTH);
go.addActionListener(this);
}
public static void main(String[] args){
LayoutM ob = new LayoutM();
ob.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
ob.setVisible(true);
ob.setSize(300,400);
ob.setResizable(false);
ob.setLocationRelativeTo(null);
}
public void actionPerformed(ActionEvent event){
try{
answer.setText(" ");
num11 = Integer.parseInt(num1.getText());
num22 = Integer.parseInt(num2.getText());
for(int count = 1; count < num22+1;count++){
answer.append(num11+ " X "+ count+" = " + num11*count+" \n");
}
}catch(Exception e){
JOptionPane.showMessageDialog(null, "No decimals allowed");
}
}
}

You should put the answer object into a new JScrollPane object, and add the scroll pane to your LayoutM.
So, in your fields you should add:
private JScrollPane scroll;
Instead of using
add(answer,BorderLayout.SOUTH);
You should use
add(scroll,BorderLayout.SOUTH);
And in your actionPerformed() method, you should change the number of rows according to the number you got from the user. Put this before the for loop:
if ( num22 > 20 ) {
answer.setRows(num22);
} else {
answer.setRows(20);
}