Develop 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);
}

Why is my ItemListener program not allowing me to select an option from two different JComboBoxes in Java?

My program will only do one JcomboBox at a time when I am trying to get both numbers to be added together to display the final number.
It allows me to run the program, but it will not display the final price because it does not want to select two things at once.
Here is the code for my program:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class CottageRental2 extends JFrame implements ItemListener{
// Declare all instance data (primitives and objects used)
private int WIDTH = 676;
private int HEIGHT = 321;
Container con;
private JLabel label1;
private JLabel label2;
private JLabel label3;
JComboBox cbox1;
JComboBox cbox2;
String [ ] roomChoice = {"1 Bedroom: $600","2 Bedroom: $800","3 Bedroom: $1000"};
String [ ] activityChoice = {"Horse Back Riding: $60","Rafting: $40","Row Boat Rental: $50"};
ImageIcon icon1 = new ImageIcon("C:\\Users\\Coding\\Desktop\\cottage.jpeg");
Font f1 = new Font("Ariel", Font.BOLD, 30);
//constructor
public CottageRental2(){
super("Cottage Rental");
con = getContentPane();
con.setLayout(new BorderLayout());
con.setBackground(Color.GRAY);
setSize(WIDTH, HEIGHT);
setVisible(true);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
public void createGUI(){
label1 = new JLabel("Woodberry Cottage Rental", JLabel.CENTER);
label1.setFont(f1);
label1.setForeground(Color.WHITE);
label2 = new JLabel("Rental Amount Due: $660", JLabel.CENTER);
label2.setFont(f1);
label2.setForeground(Color.WHITE);
label3 = new JLabel(icon1);
cbox1 = new JComboBox();
cbox1.addItem(roomChoice[0]);
cbox1.addItem(roomChoice[1]);
cbox1.addItem(roomChoice[2]);
cbox1.addItemListener(this);
cbox2 = new JComboBox();
cbox2.addItem(activityChoice[0]);
cbox2.addItem(activityChoice[1]);
cbox2.addItem(activityChoice[2]);
cbox2.addItemListener(this);
con.add(label1, BorderLayout.NORTH);
con.add(label2, BorderLayout.SOUTH);
con.add(label3, BorderLayout.CENTER);
con.add(cbox1, BorderLayout.WEST);
con.add(cbox2, BorderLayout.EAST);
}
public void itemStateChanged(ItemEvent event){
Object source = event.getSource();
int price1 = 0;
int price2 = 0;
if(source == cbox1){
int roomIndex = cbox1.getSelectedIndex();
if(roomIndex == 0){
price1 = 600;
}
if(roomIndex == 1){
price1 = 800;
}
if(roomIndex == 2){
price1 = 1000;
}
}
if(source == cbox2){
int activityIndex = cbox2.getSelectedIndex();
if(activityIndex == 0){
price2 = 60;
}
if(activityIndex == 1){
price2 = 40;
}
if(activityIndex == 2){
price2 = 50;
}
}
label2.setText("Rental Amount Due: $" + (price1 + price2));
}
public static void main(String[] args){
CottageRental2 object = new CottageRental2();
object.createGUI();
object.setSize(675, 320);
}
}

Your problem is your if (source == ...) if blocks which prevent the program from getting the selected item from the other JComboBox, the one that isn't being actively selected.
One solution: get rid of the offending if blocks that test for the source of the event in the listener:
public void itemStateChanged(ItemEvent event) {
// Object source = event.getSource();
int price1 = 0;
int price2 = 0;
// if(source == cbox1){
int roomIndex = cbox1.getSelectedIndex();
if (roomIndex == 0) {
price1 = 600;
} else if (roomIndex == 1) {
price1 = 800;
} else if (roomIndex == 2) {
price1 = 1000;
}
// }
// if(source == cbox2){
int activityIndex = cbox2.getSelectedIndex();
if (activityIndex == 0) {
price2 = 60;
} else if (activityIndex == 1) {
price2 = 40;
} else if (activityIndex == 2) {
price2 = 50;
}
// }
label2.setText("Rental Amount Due: $" + (price1 + price2));
}
Also, it would be safer if you use some else if blocks in your item selection statements.

Java NPE with .split

I'm fairly new with Java, (and this site) so I'm not sure what to do with this "issue"...
I'm not sure whether to put my entire code in this or not...So I'll just put what I think is causing the issue. The program compiles perfectly, except when I try to run it. That's when I get a Null Pointer Exception at line 96. I have no idea why this is happening.
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.io.*;
public class LicensePlateGeneratorTemplate extends JFrame implements ActionListener{
private JTextArea txtOutput;
private JTextField txtNumPlates;
private JButton btnDisplay;
private JLabel lblTitle, lblInstruction;
private PrintWriter output;
private String letters, numbers, fileName;
private int randomLetter, randomNumber, numPlates;
private String [] a, b ;
private String [] lttrArray, nmbrArray;
public static void main(String[] args) throws IOException{
new LicensePlateGeneratorTemplate();
}
public LicensePlateGeneratorTemplate() throws IOException{
//label thast contains number of licence plates generated
txtNumPlates = new JTextField();
txtNumPlates.setBounds(320, 60, 28, 28);
lblInstruction = new JLabel("How many license plates would you like to generate?");
lblInstruction.setBounds(15, 60, 300, 28);
//A random number generator in the action performed method should allow you to select a random letter from the letters String
//then a random number from the numbers String
String letters = "A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Z";
String numbers = "1,2,3,4,5,6,7,8,9,0";
lttrArray = letters.split (",");
nmbrArray = numbers.split (",");
System.out.println(lttrArray[20] + lttrArray [10]);
System.out.println(nmbrArray[3]+ nmbrArray [5]);
fileName = "licensePlates.txt";
output = new PrintWriter(new FileWriter(fileName));
lblTitle = new JLabel();
lblTitle.setFont(new Font("Britannic Bold", Font.BOLD, 28));
lblTitle.setText("License Plate Generator");
lblTitle.setBounds(30, 10, 400, 50);
JPanel panel = new JPanel();
panel.setLayout(null);
//JTextArea
txtOutput = new JTextArea();
txtOutput.setBounds(60, 150, 275, 196);
txtOutput.setEditable(true);
//generate button properties
btnDisplay = new JButton();
btnDisplay.setText("Generate");
btnDisplay.setBounds(150, 100, 100, 40);
btnDisplay.setFocusable(true);
btnDisplay.addActionListener(this);
//add components to the panel
panel.add(btnDisplay);
panel.add(txtOutput);
panel.add(lblTitle);
panel.add(lblInstruction);
panel.add(txtNumPlates);
//frame properties
setContentPane(panel);
setSize(400, 400);
setTitle("License Plate Generator");
setLocationRelativeTo(null);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setResizable(false);
setVisible(true);
}
public void actionPerformed (ActionEvent e)
{
if (e.getSource() == btnDisplay)
{
//change number user inputs into a int value
int userNum = Integer.parseInt(txtNumPlates.getText ());
for (int k = 0; k <= userNum; k ++)
{//number of licence places that are being made
for (int i = 0; i < 4; i ++)//loop for letters produced
{
int randLtr = 0 + (int)(Math.random() * ((24 - 0) + 1));
a [i] = lttrArray [randLtr];
output.println (a[i]);
txtOutput.insert(a[i] + "\n", 0);
}
for (int j = 0; j < 3; j++)//loop for number produced
{
int randNum = 0 + (int)(Math.random() * ((9 - 0) + 1));
b [j] = nmbrArray [randNum];
output.println (b[j]);
txtOutput.insert(b[j] + "\n", 0);
}
output.close();//closes fileWriter
}//end of userNum loop
}//end of e.getsource
}
}
Edit: Added full code.

Since lttrArray is clearly non-null (unless you're assigning it as lttrArray = null somewhere in the snipped code), I would guess that a is null.

for loop for array only processing one element in java?

I can't figure out why whenever I cycle through my array using the for-loop it only produces one element (the first) to console? I'm pretty sure it's a rookie-mistake I'm looking over, so any tips and suggestions would help.
I'm making a program for fun that compares two strings typed in a text field and if they don't exist in the array it produces a JOPtionPane message on the contrary. It's for a battle-hack I may produce in the future for vBulletin forum, but I'm messing around with algorithms before I move to that step. Thanks, guys!
package battleoptionspart1;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import java.lang.*;
import javax.swing.border.*;
public class BattleOptionsPart1 extends JFrame{
JButton newthread, previewpost;
JRadioButton battle1;
JTextField postcount, oppA, oppB;
JLabel battle2, max;
JPanel panel;
String [] array = {"Bill","Tom","Wendy", "Paula"};
public BattleOptionsPart1 () {
panel = new JPanel();
Toolkit tool = Toolkit.getDefaultToolkit();
Dimension dim = tool.getScreenSize();
this.setSize(500, 500);
this.setTitle("Battle Options");
GridLayout grid = new GridLayout(0,1,2,2);
this.setLayout(grid);
newthread = new JButton("Post New Thread");
previewpost = new JButton("Preview Post");
postcount = new JTextField("", 4);
oppA = new JTextField("",10);
oppB = new JTextField("",10);
battle1 = new JRadioButton();
battle2 = new JLabel("Would you like to start a recorded battle?");
max = new JLabel("Enter max post count user must have to vote");
ListenForButton listen = new ListenForButton();
newthread.addActionListener(listen);
previewpost.addActionListener(listen);
JPanel opponents = new JPanel();
Border oppBorder = BorderFactory.createTitledBorder("Battlers");
opponents.setBorder(oppBorder);
opponents.add(oppA);
opponents.add(oppB);
JPanel battle = new JPanel();
Border battleBorder = BorderFactory.createTitledBorder("Start Battle");
battle.setBorder(battleBorder);
battle.add(battle1);
battle.add(battle2);
JPanel buttons = new JPanel();
Border buttonBorder = BorderFactory.createTitledBorder("Create Thread");
buttons.setBorder(buttonBorder);
buttons.add(newthread);
buttons.add(previewpost);
JPanel restriction = new JPanel();
Border resBorder = BorderFactory.createTitledBorder("Restrictions");
restriction.setBorder(buttonBorder);
restriction.add(postcount);
restriction.add(max);
this.add(opponents);
this.add(battle);
this.add(restriction);
this.add(buttons);
this.add(panel);
int xPos = (dim.width / 2) - (this.getWidth() / 2);
int yPos = (dim.height / 2) - (this.getHeight() / 2);
this.setLocation(xPos,yPos); //places form in the middle
this.setVisible(true); // users can see form
this.setResizable(false); //users can't resize the form
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
private class ListenForButton implements ActionListener {
#Override
public void actionPerformed(ActionEvent e) {
String compareA = oppA.getText();
String compareB = oppB.getText();
if (e.getSource() == newthread)
{
System.out.println(compareA + "\n" + compareB);
for(int j = 0; j < array.length; j++)
{
System.out.println(array[j]);
if(!compareA.equals(array[j]))
{
JOptionPane.showMessageDialog(null, compareA + " doesn't exist!", "Error Message", JOptionPane.ERROR_MESSAGE);
oppA.requestFocus();
break;
}
if (!compareB.equals(array[j]))
{
JOptionPane.showMessageDialog(null, compareB + " doesn't exist!", "Error Message", JOptionPane.ERROR_MESSAGE);
oppB.requestFocus();
break;
}
else
{
JOptionPane.showMessageDialog(null, "New thread created successfully!", "Success", JOptionPane.INFORMATION_MESSAGE);
break;
}
}
}
else if (e.getSource() == previewpost)
{
System.exit(0);
}
}
}
public static void main(String[] args) {
BattleOptionsPart1 battle = new BattleOptionsPart1();
}
}

In each of the possible options in your loop, you use break, which leaves the loop immediately. If you remove those statements, you'll process each object in the array.
If you want to check if there's a match, you need to go through every element and do your processing after going through the whole array. Here is an example for an array of type int:
boolean contains = false;
for (int i = 0; i < arr.length; i++)
{
if (arr[i] == searchKey)
{
contains = true;
break;
}
}

You're breaking out of the loop. with the break; command after the first array element