I am trying to update a JLabel by using the setText() method, but I can't redraw JLabel. Do I have to use the repaint() method to do that?
Here is the part of code, I do not get any errors, but it is not updating the JLabel.
public void actionPerformed(ActionEvent e) {
fc = new JFileChooser();
if(e.getSource() == addButton) {
int returnVal = fc.showOpenDialog(Main.this);
if (returnVal == JFileChooser.APPROVE_OPTION) {
filesList = fc.getSelectedFiles();
setFilesList(filesList);
StringBuilder logString = new StringBuilder();
logString.append("Files to Convert " + "\n");
for(int i = 0; i < getFiles().length; i++) {
logString.append(filesList[i].getAbsolutePath());
}
//JLabel log = new JLabel(); created above.
log.setText(logString.toString());
} else {
//log.append("Open command cancelled by user." + newline);
}
//log.setCaretPosition(log.getDocument().getLength());
}
}
JLabel requires no repaint call. Simply calling setText(...) will change the label's text, and that is all that is required.
I wonder if your problem is a concurrency issue, that you are doing a long-running process on the Swing event thread and that this is preventing your label from updating its text.
If so, then consider doing your long-running process in a background thread such as that provided by a SwingWorker, and then updating your JLabel's text on the Swing thread, such as can be done via the SwingWorker's publish/process methods.
For more on this, please have a look at the Lesson: Concurrency in Swing tutorial.
Also Mario De... is correct about not being able to print simple new-lines on a JLabel. 1+ to his answer.
I'm a bit stumped on how the repainting of frames/component works in Java. You can Paint(Graphics g), update(Graphics g) which according to the javadoc just calls paint(g). Finally there's also repaint()...
If none of those seem to work, wouldn't it just be easier to create the label only at the line where you are currently trying to set the text?
Edit: there is also the option of using an ineditable textArea. Not only can it display the standard newline character, but you can put it in a jScrollPane, which is handy when you have lots of files in the log, and you don't need to repaint text components to display updated text. The bonus is magnificent imo...
This simple example works for me so problem is not JLabel but some bug in other part of your source code. Please post full source code.
import java.awt.BorderLayout;
import java.awt.Button;
import java.awt.GridLayout;
import java.awt.Panel;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JFrame;
import javax.swing.JLabel;
public class Application {
public static void main(String[] args) {
JFrame frame = new JFrame("JLabel test");
frame.setVisible(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
Panel p = new Panel();
p.setLayout(new GridLayout());
Button button = new Button("Change");
final JLabel label = new JLabel(Long.toString(Long.MAX_VALUE));
button.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
label.setText(Long.toString(e.getWhen()));
}
});
p.add(button);
p.add(label);
frame.add(p, BorderLayout.NORTH);
frame.pack();
}
}
I have run into a similar problem. I tried to setText("Good Bye") in actionPerformed() in an exit button ActionListener before disposing my JFrame right there, but the text was not changing.
Eventually I realized that my label was not getting updated as I was disposing the frame in the anonymous ActionListener class. After I had let the code leave ActionListener.actionPerformed(), the label text got updated.
I had to dispose my JFrame in a new thread though to ensure that:
actionPerformed is finished so that the main thread returns from the anonymous nested class and updates the label in the main class.
A new thread is started which waits for a second to allow "Good Bye" to be read.
This new thread the disposes the frame.
repaint() won't work here.
Simply use label_name.paintImmediately(label_name.getVisibleRect());
It will get updated right away.
Please try -
jlabel.setText("Your Text");
jLabel.setVisisble(true);
Related
I have a Java program where I plan to take input from GUI, and use that input later for processing in main(). I am using Eclipse.
I am sending an HW object(called HWObj) to the GUI JFrame, and checking for a boolean field in the object to continue processing in main().
InputWindow is custom object which extends JPanel implements ActionListener
It contains a reference to the current JFrame(parentFrame). On clicking a JButton in InputWindow, I have written a custom ActionListener which sets the value of HWObj.check to true and disposes the parentFrame. This should cause execution to resume in main().
Code for HW class is as below :
import java.awt.*;
import javax.swing.*;
public class HW {
//globals
boolean check;
public HW() {
//initialisations
check = false;
}
public static void main(String args[]) {
final HW problem = new HW();
try {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
//Create and set up the window.
JFrame frame = new JFrame("Select folders");
frame.setPreferredSize(new Dimension(640, 480));
frame.setResizable(false);
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
InputWindow Directories = new InputWindow(problem, frame);
Directories.setOpaque(true);
frame.add(Directories);
//Display the window.
frame.pack();
frame.setVisible(true);
}
});
} catch(Exception e) {
System.out.println("Exception:"+e.getLocalizedMessage());
}
while(!problem.finish);
//Do processing on problem
System.out.println("Done");
}
}
The Actionlistener in the gui is as follows:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class InputWindow extends JPanel
implements ActionListener {
private static final long serialVersionUID = 4228345704162790878L;
HW problem;
JFrame parentFrame;
//more globals
public InputWindow(HW problem, JFrame parentFrame) {
super();
this.setLayout(new GridBagLayout());
GridBagConstraints gbc = new GridBagConstraints();
this.parentFrame = parentFrame;
this.problem = problem;
JButton finishButton = new JButton("Finish");
finishButton.setActionCommand("fin");
finishButton.addActionListener(this);
gbc.gridx = 0;
gbc.gridy = 0;
this.add(finishButton, gbc);
//Initialize buttons and text areas and labels
//Code removed for ease of reading
}
public void actionPerformed(ActionEvent e) {
String command = e.getActionCommand();
if(command.equals("fin")) {
//Do a lot of stuff, then
this.removeAll();
parentFrame.dispose();
problem.check = true;
}
}
}
I have checked, and the control to this function comes normally on button click.
Now, I would expect it to return to main, and exit the while loop, and continue processing.
This does not happen. The debugger in eclipse shows only the main thread running, and when I try to pause it, I see that the thread is stuck in the while loop. But if I try to step through, it exits the while loop as expected, and continues. However, it gets remains stuck in the while loop until I manually try to debug it.
What is the problem? Why is it not resuming the main thread as expected?
How do I resolve this issue?
Your problem is to do with how the Java memory model works. The loop in your main thread will be checking a stale value of check.
When you enter the debugger, the memory is forced to be updated, so that's why it starts working at that point.
If you mark your variable as volatile, that will force the JVM to ensure that all threads are using the up-to-date value:
volatile boolean check;
You can read more about volatile and the Java memory model in the documentation.
It looks like you're using a JFrame where you should be using a modal JDialog. If you use the modal JDialog for an input window, you will know exactly when it is "finished" since code flow will resume from the calling code from right after when the dialog was set visible.
Either that or if you are trying to swapviews, then use a CardLayout to swap your view, and use an observer type pattern to listen for change of state.
I have an application working in Java Swing, but can't seem to convert to an Applet. Basically there are four buttons displayed on the Applet, and I want one of them to clear the screen and then draw a new interface (I'm going to add stuff for the other buttons, of course, but I got stuck here).
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.JApplet; //import swing applet interface
import java.util.Hashtable;
public class TopMenu extends JApplet{
private JPanel panel = new JPanel();
public void init(){
mainMenu();
}
public void mainMenu() {
// create buttons
panel.setLayout(new GridLayout(2, 2));
JButton collectButton = new JButton("Collect data");
JButton uploadButton = new JButton("Upload");
JButton downloadButton = new JButton("Download");
JButton exploreButton = new JButton("Explore data");
panel.add(collectButton);
panel.add(uploadButton);
panel.add(downloadButton);
panel.add(exploreButton);
collectButton.addActionListener(new ActionListener( ) {
public void actionPerformed(ActionEvent e) {
int numberGFish = 400;
//panel.removeAll();
//panel.add(new JLabel("Just to test"), BorderLayout.CENTER);
//panel.revalidate();
//panel.repaint();
}
});
setContentPane(panel);
}
}
All the code works totally fine until I add the ActionListener, and then the whole thing just goes blank. It compiles okay, but when I test it on my server not even the first menu comes up, it's just a blank panel. I've tried putting loads of really banal things in the ActionListener bit to make sure it's not a problem with them, but as you can see even just declaring a number in there doesn't work.
Originally I actually had the Listener bit call on another method which then did everything else, and that didn't work either, I scrapped that because I thought perhaps that was the problem.
I'm sure this is so simple but I've sunk many hours into it now and I've really just run out of ideas of things to test. And advice gratefully appreciated.
Don't know if it would be a problem or not but all GUI components should be created on the Event Dispatch Thread.
Here is the recommended code structure from the Swing tutorial on How to Make Applets:
public void init() {
//Execute a job on the event-dispatching thread:
//creating this applet's GUI.
try {
javax.swing.SwingUtilities.invokeAndWait(new Runnable() {
public void run() {
createGUI();
}
});
} catch (Exception e) {
System.err.println("createGUI didn't successfully complete");
}
}
private void createGUI() {
JLabel label = new JLabel(
"You are successfully running a Swing applet!");
label.setHorizontalAlignment(JLabel.CENTER);
label.setBorder(BorderFactory.createMatteBorder(1,1,1,1,Color.black));
add(label, BorderLayout.CENTER);
}
I knew it was a dumb question, but I just couldn't figure it out. I've sorted it now.
I was being totally daft and not copying across the TopMenu$1.class file to the server. For some reason it works without this file but not with the ActionListener bit added. So I never thought that could be the problem.
Doh! Thanks all.
I found this code here: how to display console output in java JTextarea one by one in a loop when button action is triggered
and it displays console output in a jtextarea.
I have added this class as action in a jmenuitem. So that it appears when I want and when I run other classes it will show the output there. However when I launch it, it works properly, but if I try and launch another class which will show output in console and accept userinput, the jtextarea which is supposed to show console output at the same time, it freezes. How could I make it so that it stays tuned, despite invoking other classes/frames? Thanks in advance
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class DynamicWrite implements ActionListener
{
JFrame frame = new JFrame("TextArea");
JTextArea tArea = new JTextArea(10,20);
JButton button = new JButton("Click");
JScrollPane pane = new JScrollPane(tArea);
SwingWorker worker;
String s= "Java is an Object Oriented Programming langauge...Java is static typed language...asbfldfjsdj";//some random String
public void prepareAndShowGUI()
{
Container container = frame.getContentPane();
container.add(pane);container.add(button,BorderLayout.NORTH);
tArea.setLineWrap(true);
tArea.setWrapStyleWord(true) ;
button.addActionListener(this);
frame.pack();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
public void actionPerformed(ActionEvent evt)
{
if(evt.getSource()==button)
{
tArea.setText("");
if (worker!=null)
{
worker.cancel(true);
}
worker = new SwingWorker()
{
#Override
protected Integer doInBackground()//Perform the required GUI update here.
{
try
{
for(int i = 0;i<s.length();i++)
{
tArea.append(String.valueOf(s.charAt(i)));
Thread.sleep(5);
}
}catch(Exception ex){}
return 0;
}
};
worker.execute();//Schedules this SwingWorker for execution on a worker thread.
}
}
public static void main(String st[])
{
DynamicWrite dyna = new DynamicWrite();
dyna.prepareAndShowGUI();
}
}
The example you have (apart from from being a bad example as outlined by Hovercraft Full of Eels) has nothing to do with redirecting console output.
If you want to redirect the standard out to the text area, take a look at How to set output stream to TextArea for an example
If you want to redirect the output of some other process, then you can only do this if you've launched the process yourself, there's no (easy way that I know of) to connect to the standard out/in of another running process (that your program didn't start itself directly)
Check out Printing a Java InputStream from a Process for an example
I have a frame, where i load a panel into. It works fine, but nothing has focus when it loads. Pressing tab doesn't help. I have to use the mouse to press a textfield.
I've tried: jtextfield1.requestFocus(); and jtextfiel1.requestFocusInWindow(); But it doesn't work.
What am I doing wrong?
The constructor in the JPanel:
public OpretOpdater(BrugerHandler brugerHandler, ReklamationHandler reklamationsHandler) {
initComponents();
jTextFieldOrdnr.requestFocusInWindow();
this.brugerHandler = brugerHandler;
this.rekH = reklamationsHandler;
startUp();
}
Putting the panel in the frame in the GUI:
public static void opret(ReklamationHandler reklamationHandler) {
rHandler = reklamationHandler;
SwingUtilities.invokeLater(opret);
}
static Runnable opret = new Runnable() {
#Override
public void run() {
JFrame f = jframe;
f.getContentPane().removeAll();
JPanel opret = new OpretOpdater(bHandler, rHandler);
f.getContentPane().add(opret);
f.pack();
f.setLocationRelativeTo(null);
}
};
You should call requestFocusInWindow() only when components are visible/shown on a container or after pack() has been called and all components are added to the container or else it wont work.
Also please be sure to create Swing components on Event Dispatch Thread. If you haven't already have read on Concurrency in Swing.
The reason I mention the above is not creating and manipulating Swing components on the EDT can cause random artifacts in the code. i.e focus is not being given etc.
This code below was created to show how calling requestFocusInWindow before a component is visible will not work but calling it after its visible works as expected.
Also note that removing the SwingUtilities block will cause the requestFocusInWindow not to work as expected (i.e we might be given focus or not depending on our luck :P):
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
public class Test {
public Test() {
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
JTextField f1 = new JTextField(10);
JTextField f2 = new JTextField(10);
//f2.requestFocusInWindow(); //wont work (if uncomment this remember to comment the one after setVisible or you wont see the reults)
JButton b = new JButton("Button");
JPanel p = new JPanel();
p.add(f1);//by default first added component will have focus
p.add(f2);
p.add(b);
frame.add(p);
//f2.requestFocusInWindow();//wont work
frame.pack();//Realize the components.
//f2.requestFocusInWindow();//will work
frame.setVisible(true);
f2.requestFocusInWindow();//will work
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {//if we remove this block it wont work also (no matter when we call requestFocusInWindow)
#Override
public void run() {
new Test();
}
});
}
}
I would suggest a read on How to Use the Focus Subsystem.
Often it is nice to indicate which field you want to have focus when you create the field and not separate the code by adding the request focus when the frame becomes visible.
Take a look at Dialog Focus which has a solution that is also applicable in this case. Using this approach your code would look like:
JTextField f2 = new JTextField(10);
f2.addAncestorListener( new RequestFocusListener() );
I've looked at other JLabel threads and though similar, a few just don't seem to apply to what I'm experiencing. First, I want to say I am a novice when it comes to Java. Next, I am trying to follow tutorials and demos at the docs.oracle.com site. Now, I can update the label when I type something into a JTextField and there is an ActionListener on that...
But I also have a Menu, and when I select a Menu Item, that Action does not want to update the label.
Questions -
How do I have action listeners on both JTextFields and JMenuItems? Are there two ActionEvent methods or do I use one method and somehow identify each type of action?
If I use the same basic code in the JTextField ActionEvent and JMenuItem ActionEvent, the JLabel updates correctly with the JTextField event but not JMenuItem event. They both use the messageField.setText property. Could the JMenuItem action be doing something to block the setText?
I can easily copy code in here, but it's pretty spaghetti-like at the moment, so if you want to see anything, let me know specifically and I'll post it.
I would appreciate any assistance that anyone would be able to provide.
---edit---
Wow!! Thanks for all of the comments and suggestions.
1 - I know it has to be my code. As I mentioned, I am really just cobbling stuff together from demos and tutorials, and trying to learn Java along the way. I've just never gotten the hang of object oriented....
2 - I do know the individual Listeners are working. I'm using System.out.println to validate, as well as inspecting those labels in debug mode to see they have indeed changed.
3 - I will look at the various links and code posted here and see if I can figure out what's wrong with my code.
Really, thanks again!
---edit---
Here is what I originally had in my createAndShowGUI method....
private static void createAndShowGUI()
{
JFrame frame = new JFrame("Create XML for Photo Gallery");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
CreateGalleryXML window = new CreateGalleryXML();
frame.setJMenuBar(window.createMenuBar());
frame.add(new CreateGalleryXML());
frame.pack();
frame.setVisible(true);
}
Seems like you yourself are doing something wrong, in your code. Without a proper SSCCE it's hard to say what thing you doing wrong, since it works perfectly, using same ActionListener for both JMenuItem and JTextField.
Here is a sample program to match with yours :
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class UpdateLabel
{
private JLabel label;
private String labelText;
private ActionListener action = new ActionListener()
{
public void actionPerformed(ActionEvent ae)
{
setLabelText((String) ae.getActionCommand());
label.setText(getLabelText());
}
};
private void setLabelText(String text)
{
labelText = text;
}
private String getLabelText()
{
return labelText;
}
private void createAndDisplayGUI()
{
final JFrame frame = new JFrame("Update Label");
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
frame.setLocationByPlatform(true);
JMenuBar menuBar = new JMenuBar();
JMenu programMenu = new JMenu("Program");
JMenuItem exitMenuItem = new JMenuItem("Exit");
exitMenuItem.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent ae)
{
frame.dispose();
}
});
JMenu labelMenu = new JMenu("Label");
JMenuItem updateMenuItem = new JMenuItem("Update Label");
updateMenuItem.setActionCommand("Updated by JMenuItem");
updateMenuItem.addActionListener(action);
programMenu.add(exitMenuItem);
labelMenu.add(updateMenuItem);
menuBar.add(programMenu);
menuBar.add(labelMenu);
frame.setJMenuBar(menuBar);
JPanel contentPane = new JPanel();
label = new JLabel("I am the LABEL which will be updated!!");
contentPane.add(label);
JTextField tfield = new JTextField(10);
tfield.setActionCommand("Updated by JTextField");
tfield.addActionListener(action);
frame.add(contentPane, BorderLayout.CENTER);
frame.add(tfield, BorderLayout.PAGE_END);
frame.pack();
frame.setVisible(true);
}
public static void main(String... args)
{
SwingUtilities.invokeLater(new Runnable()
{
public void run()
{
new UpdateLabel().createAndDisplayGUI();
}
});
}
}
And here is the output in both the cases :
and
Do check out the main method, might be you had failed to put your code inside EDT - Event Dispatcher Thread, that can lead to such issues too. All updates on the Swing GUI, must be done on the Event Dispatcher Thread.
LATEST EDIT
It seems to me that CreateGalleryXML extends JPanel by the look of it. See at Line 3 of this below code taken from your update, here you are initializing a new Object of CreateGalleryXML inside, when you already had one Object window created at Line 1:
CreateGalleryXML window = new CreateGalleryXML();
frame.setJMenuBar(window.createMenuBar());
frame.add(new CreateGalleryXML());
So try to change the above thingy to this
CreateGalleryXML window = new CreateGalleryXML();
frame.setJMenuBar(window.createMenuBar());
frame.add(window);
and see what happens and Please do revert back again :-)
Use Action to encapsulate common functionality that must be shared by menus and related components. See this example that extends AbstractAction.
Pretty much everything you could need to know is in the Java tutorials. Down the bottom they have demo's on how to do both menu's and text fields. They include source code to look at as well.
There's not much more I can say that they don't say better, but in answer to your questions:
Both, you can have separate listener's on each component, or one that figures out what component is responsible for causing the action event. I would suggest you use separate ones for each thing.
Can't really say with out seeing the code, are you sure that the action on the JMenu is even firing? Does it print something to the console etc if you use System.out.println somewhere?