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Prevent more than one DialogBox to appear

import java.awt.event.*;
import java.awt.*;
import javax.swing.*;
class Demo implements ActionListener
{
JFrame f;
JButton b;
DisplayDialog dialog;
public Demo()
{
f = new JFrame();
f.setSize(200,200);
b = new JButton("Click me");
f.add(b);
dialog = new DisplayDialog();
b.addActionListener(this);
f.setVisible(true);
}
public void actionPerformed(ActionEvent e)
{
Object o = e.getSource();
if(o==b)
{
dialog.display("Hello");
dialog.display("Hello");
dialog.display("Hello");
dialog.display("Hello");
dialog.display("Hello");
}
}
public static void main(String args[])
{
Demo d = new Demo();
}
class DisplayDialog implements ActionListener
{
JDialog dg;
JLabel l;
JButton b;
Font myfont;
public DisplayDialog()
{
dg = new JDialog(f,"Alert!",true);
dg.setSize(300,150);
l = new JLabel("Message");
b = new JButton("OK");
myfont = new Font("Serif",Font.BOLD,12);
l.setFont(myfont);
dg.add(l);
dg.add(b,"South");
dg.setDefaultCloseOperation(JFrame.HIDE_ON_CLOSE);
b.addActionListener(this);
}
public void actionPerformed(ActionEvent e)
{
Object o = e.getSource();
if(o==b)
{
dg.setVisible(false);
}
}
public void display(String str)
{
if(dg.isVisible())
dg.setVisible(false);
l.setText(str);
dg.setVisible(true);
}
}
}
When the button is clicked, 5 Dialog box appears. Now I want to make such a change in the DisplayDialog class so that every time display method is called,the previously opened dialogs are closed and the latest one is the only one that is visible.
I tried doing this :
public void display(String str)
{
if(dg.isVisible())
dg.setVisible(false);
l.setText(str);
dg.setVisible(true);
}
but it didn't do anything.
Also,I am very surprised that multiple dialog boxes are appearing even though there is only one instance of the object. From my understanding, setVisible(true) should not do anything if the dialog is already visible.
This whole situation is very confusing to me.

The thing is that you cannot do this in single thread (like you are preseting it in your demo) - setVisible will always block (wait till dialog closes) and another display call will not be invoked till then.
Try to run it in multi frame env (like you have stated that your app is) but change display to
public void display(String str){
l.setText(str);
if(dg.isVisible()){
dg.setVisible(true);
}
}
This way dialog will not be displayed if it is already visible, but text will be changed. The condition for it to work is that is is not consecutinve calls to display like in demo, but from different threads. There is no other way around. setVisible will alwys block.

Accessing data from another class which reads values

Ok, so here is a problem: I have main class which generates a window and two buttons:
...
public MainWindow()
{
...
b_read.addActionListener(new ReadStudents());
b_open_all.addActionListener(new OpenStudents());
...
In ReadStudents.java class I load data from a file with JFileChooser and print it on the screen. Sample of code thats load file:
#Override
public void actionPerformed(ActionEvent e) {
...
JFileChooser fc = new JFileChooser(".");
...
int rez = fc.showOpenDialog(fc);
if (rez == JFileChooser.APPROVE_OPTION) {
file = fc.getSelectedFile();
...
So now in my ReadStudents.java class variable "file" has my loaded information.
How do i pass this variable with containing information in it to a class that prints Students on the screen (second button OpenStudents.java) ?
Edit:1) I can not initialize an object of ReadStudents.java in OpenStudents.java class because in the new object variable "file" will be empty. Something is loaded to a "file" only when a button b_read is pressed.

One option would be to implement the action listener on your MainWindow class and the call a method in the ReadStudents/OpenStudents that return the list of files.
For example:
/**
* Main window class.
*/
public static void main(String args[]) {
JFrame mainFrame = new JFrame();
mainFrame.setLayout(new BorderLayout());
mainFrame.setSize(100, 100);
final StudentReader student = new StudentReader();
JButton button = new JButton("Click Me");
button.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
// Make the call here. Take note!
// Look at the return type!
List<String> strings = student.fileNames();
for (String s : strings) {
System.out.println(s);
}
}
});
mainFrame.add(button);
mainFrame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
mainFrame.setVisible(true);
}
public class StudentReader {
public List<String> fileNames() {
// Do your magic here :)
// Open a dialog. Get the files.
// Return it as a list
return Arrays.asList(new String[]{"Filename"});
}
}
I Hope this helps!

Java JTextField information access from another class

I am using a gui with JTextFields to collect some information and then a JButton that takes that infomration and writes it to a file, sets the gui visibility to false, and then uses Runnable to create an instance of another JFrame from a different class to display a slideshow.
I would like to access some of the information for the JTextFields from the new JFrame slideshow. I have tried creating an object of the previous class with accessor methods, but the values keep coming back null (I know that I have done this correctly).
I'm worried that when the accessor methods go to check what the variables equal the JTextFields appear null to the new JFrame.
Below is the sscce that shows this problem.
package accessmain;
import javax.swing.*;
import javax.swing.border.EmptyBorder;
import java.awt.*;
import java.awt.event.*;
import java.io.*;
public class AccessMain extends JFrame implements ActionListener
{
private static final int FRAMEWIDTH = 800;
private static final int FRAMEHEIGHT = 300;
private JPanel mainPanel;
private PrintWriter outputStream = null;
private JTextField subjectNumberText;
private String subjectNumberString;
public static void main(String[] args)
{
AccessMain gui = new AccessMain();
gui.setVisible(true);
}
public AccessMain()
{
super("Self Paced Slideshow");
setSize(FRAMEWIDTH, FRAMEHEIGHT);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setLayout(new BorderLayout());
//Begin Main Content Panel
mainPanel = new JPanel();
mainPanel.setBorder(new EmptyBorder(0,10,0,10));
mainPanel.setLayout(new GridLayout(7, 2));
mainPanel.setBackground(Color.WHITE);
add(mainPanel, BorderLayout.CENTER);
mainPanel.add(new JLabel("Subject Number: "));
subjectNumberText = new JTextField(30);
mainPanel.add(subjectNumberText);
mainPanel.add(new JLabel(""));
JButton launch = new JButton("Begin Slideshow");
launch.addActionListener(this);
mainPanel.add(launch);
//End Main Content Panel
}
#Override
public void actionPerformed(ActionEvent e)
{
String actionCommand = e.getActionCommand();
if(actionCommand.equals("Begin Slideshow"))
{
subjectNumberString = subjectNumberText.getText();
if(!(subjectNumberString.equals("")))
{
System.out.println(getSubjectNumber());
this.setVisible(false);
writeFile();
outputStream.println("Subject Number:\t" + subjectNumberString);
outputStream.close();
SwingUtilities.invokeLater(new Runnable()
{
#Override
public void run()
{
AccessClass testClass = new AccessClass();
testClass.setVisible(true);
}
});
}
else
{
//Add warning dialogue here later
}
}
}
private void writeFile()
{
try
{
outputStream = new PrintWriter(new FileOutputStream(subjectNumberString + ".txt", false));
}
catch(FileNotFoundException e)
{
System.out.println("Cannot find file " + subjectNumberString + ".txt or it could not be opened.");
System.exit(0);
}
}
public String getSubjectNumber()
{
return subjectNumberString;
}
}
And then creating a barebones class to show the loss of data:
package accessmain;
import javax.swing.*;
import java.awt.*;
public class AccessClass extends JFrame
{
AccessMain experiment = new AccessMain();
String subjectNumber = experiment.getSubjectNumber();
public AccessClass()
{
System.out.println(subjectNumber);
}
}
Hardcoding the accessor method with "test" like this:
public String getSubjectNumber()
{
return "test";
}
Running this method as below in the new JFrame:
SelfPaceMain experiment = new SelfPaceMain();
private String subjectNumber = experiment.getSubjectNumber();
System.out.println(subjectNumber);
Does cause the system to print "test". So the accessor methods seem to be working. However, trying to access the values from the JTextFields doesn't seem to work.
I would read the information from the file I create, but without being able to pass the subjectNumber (which is used as the name of the file), I can't tell the new class what file to open.
Is there a good way to pass data from JTextFields to other classes?

pass the argument 'AccessMain' or 'JTextField' to the second class:
SwingUtilities.invokeLater(new Runnable()
{
#Override
public void run()
{
AccessClass testClass = new AccessClass(AccessMain.this); //fixed this
testClass.setVisible(true);
}
});
Then reading the value of 'subjectNumber'(JTextField value) from the 'AccessMain' or 'JTextField' in the second class:
public class AccessClass extends JFrame
{
final AccessMain experiment;
public AccessClass(AccessMain experiment)
{
this.experiment = experiment;
}
public String getSubjectNumber(){
return experiment.getSubjectNumber();
}
}
Also, you should try Observer pattern.
A simple demo of Observalbe and Observer
Observable and Observer Objects

A simple question regarding ActionListener and 'enter' key

I am working on an assignment, and I need to enter an SQL Query in a textfield. The user can either press the custom 'execute query' button, or they can press the enter key. When either of these are used, it is to trigger an ActionListener (no other listener is allowed). Is it as simple as writing:
if (e.getSource()=='querybutton' || e.getSource=='enter')
Or is there more to it than this?
As I said, it is a simple question (I know).
edit:
I would write this bit in my ActionPerformed as:
public void actionPerformed(ActionEvent e)
{
if(e.getSource()==gui.executeQueryButton || e.getSource()==gui.enter)
{
String query = gui.queryText.getText();
//more code to follow
}
}

e.getSource() actually returns the object responsible for firing the event (not the name of the variable you used when creating the control). In this case, your button. You could in principle compare e.getSource() with the actual button instances. However, are you actually adding this action listener to buttons other than those two? Presumably you'd only have to add this listener to the two buttons for which you want this behavior -- in which case you wouldn't have to have this if check.

" Is it as simple as writing:
if (e.getSource()=='querybutton' || e.getSource=='enter')"
It's not simple to write this, but rather it is wrong to write it.
For one you don't want to compare Strings with ==, for another, you don't declare Strings with single quotes, and for a third, the enter key is not obtained in this way, but rather by adding the appropriate ActionListener object to the JTextField itself, and finally there should be in a single ActionListener class that handles this action, so the if block is completely unnecessary. This can probably be best done with a small inner private ActionListener class. You'd then create one object of this class and add it as an ActionListener for the querybutton and for the JTextField.
edit 1:
A more complete example of what I mean is shown below, a demo class that has a private inner handler class:
import java.awt.event.*;
import javax.swing.*;
public class ActionListenerEg extends JPanel {
private JButton queryButton = new JButton("Query");
private JTextField textField = new JTextField("hello", 20);
public ActionListenerEg() {
QueryListener qListener = new QueryListener();
queryButton.addActionListener(qListener);
textField.addActionListener(qListener);
add(queryButton);
add(textField);
}
private class QueryListener implements ActionListener {
public void actionPerformed(ActionEvent arg0) {
String textInField = textField.getText();
System.out.println("Use text in field, \"" + textInField + "\" to call SQL query in a background SwingWorker thread.");
}
}
private static void createAndShowUI() {
JFrame frame = new JFrame("ActionListenerEg");
frame.getContentPane().add(new ActionListenerEg());
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
createAndShowUI();
}
});
}
}
The ActionListener is fired either by pressing the button or by pressing enter from within the JTextField. I'd then have in my control class, code that is called inside of the actinoPerformed method.
edit 2: Having most handler or "control" code in its own Handler or Control class can be a good idea, but it doesn't have to implement ActionListener interface itself, but rather just have the code that will be called from within the ActionListener codes. For example, here I try to put all the handler code in its own class. It will have different methods that are called for various situations. e.g.,
import java.awt.Component;
import java.awt.event.*;
import javax.swing.*;
public class ActionListenerEg extends JPanel {
private ActionListenerHandler handler;
private JButton queryButton = new JButton("Query");
private JButton displayButton = new JButton("Display");
private JTextField textField = new JTextField("hello", 20);
// pass in handler or handler
public ActionListenerEg(final ActionListenerHandler handler) {
this.handler = handler;
QueryListener qListener = new QueryListener();
queryButton.addActionListener(qListener);
textField.addActionListener(qListener);
displayButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
if (handler != null) {
handler.displayActionPerformed(e);
}
}
});
add(queryButton);
add(textField);
add(displayButton);
}
private class QueryListener implements ActionListener {
public void actionPerformed(ActionEvent e) {
if (handler != null) {
String textInField = textField.getText();
handler.doQueryAction(e, textInField);
}
}
}
private static void createAndShowUI() {
ActionListenerHandler handler = new ActionListenerHandler();
JFrame frame = new JFrame("ActionListenerEg");
frame.getContentPane().add(new ActionListenerEg(handler));
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
createAndShowUI();
}
});
}
}
class ActionListenerHandler {
public void displayActionPerformed(ActionEvent e) {
JOptionPane.showMessageDialog((Component) e.getSource(), "Display things!");
}
public void doQueryAction(ActionEvent e, String textInField) {
String text = "We will use \"" + textInField + "\" to help create and run the SQL Query";
JOptionPane.showMessageDialog((Component) e.getSource(), text);
}
}
Please ask questions if it's clear as mudd, or if anything is wrong.

Java cant write in a .txt

hello i desperately need your help,well i have a jframe with a jcombobox and 3 textfields i want anything i write in the textfields and the choice i make in the combobox to be written in a .txt i tried so many things but nothing , the file is being created as Orders.txt but remains blank :S this is my code i appreciate any help Thanks :)
public class addSalesMan extends JFrame {
private JComboBox namesJComboBox;
private JTextField text1;//gia to poso
private JTextField text2;//thn perigrafh
private JTextField text3;//kai to numero ths paragelias kai ola auta tha egrafontai sto Orders.txt
private JButton okJbutton;
private String names[] = {"Basilis Komnhnos", "Iwanna Papadhmhtriou"};
public String amount,name,description,number;
public addSalesMan() {
super("Προσθήκη παραγγελιών");
setLayout(new FlowLayout());//dialegoume to flowlayout
// TextFieldHandler handler = new TextFieldHandler(); writer.write(string);
//ftiaxonoume to combobox gia tn epilogi tou onomatos
namesJComboBox = new JComboBox(names);//orizmos JCOMBO BOX
namesJComboBox.setMaximumRowCount(2);//na emfanizei 2 grammes
add(namesJComboBox);
namesJComboBox.addItemListener(new ItemListener() {
//xeirozome to simvan edw dhladh tn kataxwrisei ston fakelo
public void itemStateChanged(ItemEvent event) {
//prosdiorizoyme an eina epilegmeno to plaisio elegxou
if (event.getStateChange() == ItemEvent.SELECTED) {
name = (names[namesJComboBox.getSelectedIndex()]);
// writer.newLine();
setVisible(true);
}
}
}); //telos touComboBOx
//dimioutgw pediou keimenou me 10 sthles gia thn kathe epilogh kai veveonomaste oti tha mporoume na ta epe3ergasoume kanontas ta editable
text1 = new JTextField("Amount",10);
add(text1);
text2 = new JTextField("Description",10);
add(text2);
text3 = new JTextField("Order Number",10);
add(text3);
TextFieldHandler handler = new TextFieldHandler();
text1.addActionListener(handler);
text2.addActionListener(handler);
text3.addActionListener(handler);
//private eswterikh clash gia ton xeirismo twn events twn text
//button kataxwrisis
okJbutton=new JButton("Καταχώρηση");
add(okJbutton);
ButtonHandler bhandler=new ButtonHandler();
okJbutton.addActionListener(bhandler);
Order order=new Order(name,amount,description,number);
Order.addOrders(name,amount,description,number);
}
private class ButtonHandler implements ActionListener{
public void actionPerformed(ActionEvent bevent ){
JOptionPane.showMessageDialog(addSalesMan.this,String.format("Η Καταχωρηση ήταν επιτυχής",bevent.getActionCommand()));
}
}
private class TextFieldHandler implements ActionListener {
//epe3ergasia twn simvantwn me kathe enter t xrhsth
public void actionPerformed(ActionEvent evt) {
String amount,description,number;
amount=text1.getText();
description=text2.getText();
number=text3.getText();
text1.selectAll();
text2.selectAll();
text3.selectAll();
}
if(evt.getSource()==text1 && evt.getSource()==text2 && evt.getSource()==text3){
JOptionPane.showMessageDialog(addSalesMan.this,String.format("Η Καταχωρηση ήταν επιτυχής",evt.getActionCommand()));
}
}
//actionperformed telos
//ean o xrhsths patisei enter sthn kathe epilogh antistixi kataxwrisi sto
}
public static void main(String args[]) {
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
new addSalesMan().setVisible(true);
}
});
}
}
The writers are in another class. Here is the relevant code:
public static void addOrders(String name,String amount,String description,String o_number){
FileOutputStream fout;
try {
FileWriter fstream = new FileWriter("Orders.txt");
if(name!=null){
BufferedWriter out = new BufferedWriter(fstream);
out.write(name);
out.write(amount);
out.write(description);
out.write(o_number);
out.write("\t\n");
out.close();
}
} catch (IOException e) {
System.err.println ("Unable to write to file");
System.exit(-1);
}
}

It looks like the main problem is that you are calling Order.addOrders() in your constructor. Instead, you should call it when a user chooses to save it's selection. I assume you would like this to happen when the user presses the button. So the code should be added in the button's ActionListener.
What you might need to try is flushing and closing the writer when a user closes your frame.
Add the following to the constructor of your frame:
addWindowListener(new WindowAdapter(){
public void windowClosing(WindowEvent e){
writer.flush();
writer.close();
}
});
The above code will flush and close the writer when a user closes the frame.
Your code is unclear, so I'm not sure where the writer variable is declared, I'm just assuming it is a class level variable.
Also, you need to open your file in 'append' mode if you want to add lines to the file instead of overwriting it every time. This can be achieved through the following:
new FileWriter(yourFilePath, true); // set append to true