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Display not Changing [duplicate]

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What is a debugger and how can it help me diagnose problems?
(2 answers)
Closed 4 years ago.
I am working on this program that calculates the Beats per Minute (BPM) when you click the button. When you click two times, it is supposed to display the current BPM, and display the new one with every click after that. What the problem is, though, is that the display isn't changing. What do I need to do?
Here is my code:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.*;
public class BPM extends JPanel implements ActionListener {
JLabel label;
public String display;
public int bpm;
public int buttonPressed;
public int time1;
public int time2;
public int time3;
public int counter[];
public void addComponents(Container pane) {
JPanel buttons = new JPanel();
JButton bpmButton = new JButton("Click");
bpmButton.setSize(new Dimension(100, 50));
bpmButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
buttonPressed++;
counter = new int[2];
if (buttonPressed == 1) {
counter[0] = (int)(System.currentTimeMillis());
} else if (buttonPressed == 2) {
counter[1] = (int)(System.currentTimeMillis());
calculateTimeBetweenClicks();
setTime();
} else {
counter[0] = counter[1];
counter[1] = (int)(System.currentTimeMillis());
calculateTimeBetweenClicks();
setTime();
}
}
});
display = "0";
label = new JLabel(display, SwingConstants.CENTER);
label.setFont(label.getFont().deriveFont(100.0f)); // original 45
pane.add(label, BorderLayout.PAGE_START);
pane.add(bpmButton, BorderLayout.CENTER);
}
// Calculates the difference between the two saved clicks
public void calculateTimeBetweenClicks() {
if (buttonPressed == 1) {
time1 = counter[0];
} else {
time1 = counter[0];
time2 = counter[1];
}
time3 = time2 - time1;
}
// Calculates the BPM and changes the display accordingly
public void setTime() {
bpm = 60000 / time3;
display = "" + bpm + "";
label.setText(display);
}
public void actionPerformed(ActionEvent e) {
// TODO Auto-generated method stub
}
public static void createAndShowGUI() {
// Creates the window
JFrame frame = new JFrame("BPM Calculator");
frame.setPreferredSize(new Dimension(300, 200)); // original (250, 130)
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
// Adds the components to the content pane
BPM window = new BPM();
window.addComponents(frame.getContentPane());
//Displays the window.
frame.pack();
frame.setVisible(true);
}
public static void main(String[] args) {
// Turns off bold text
UIManager.put("swing.boldMetal", Boolean.FALSE);
// Allows the components to be used and interacted with
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
createAndShowGUI();
}
});
}
}

The problem is in your addComponents method, you are creating a new array on each and every button click (so you end up with a new and empty array). This is throwing off your calculation. Simply move the instantiation of your array to somewhere outside of the ActionListener like this...
public void addComponents(Container pane) {
JPanel buttons = new JPanel();
counter = new int[2]; //Move this line to here...
JButton bpmButton = new JButton("Click");
bpmButton.setSize(new Dimension(100, 50));
bpmButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
buttonPressed++;
if (buttonPressed == 1) {
counter[0] = (int)(System.currentTimeMillis());
} else if (buttonPressed == 2) {
counter[1] = (int)(System.currentTimeMillis());
calculateTimeBetweenClicks();
setTime();
} //Removed the else - see edit below :-)
}
});
Additional
Your code as-is seems to get a litle confused after the 2nd click (the first BPM calculation) as it seems to take that 2nd click as the first click of the next set of 2 clicks if you get what I mean. I'm not sure if this is intended behaviour, but if not, I would reset everything in the calculateTimeBetweenClicks method after you've calculated the correct bpm ready for a new set of 2 clicks...
// Calculates the difference between the two saved clicks
public void calculateTimeBetweenClicks() {
if (buttonPressed == 1) {
time1 = counter[0];
} else {
time1 = counter[0];
time2 = counter[1];
//Reset here ready for next 2 clicks...
counter[0]=0;
counter[1]=0;
buttonPressed = 0;
}
time3 = time2 - time1;
}

Java - Why does my print statement not run

So this is my code:
System.out.println("System Exiting...");
long current = System.currentTimeMillis();
long disired = current + 4000;
boolean done = false;
while (!done)
{
current = System.currentTimeMillis();
if (current == disired)
{
done = true;
System.exit(0);
}
}
My problem is that the print statement doesn't run, well it does run, but it runs at the same time as the exit statement, so you don't see it
[EDIT] Ok, so i just ran this code in its own file(with nothing else), and it works as i want, it prints "system Exiting..." it waits 4 seconds, and the code exits.
so it has to be something to do with the fact that i have this code inside an event listener

Your if condition is much too restrictive since your code will almost never get the times to be exactly equal, but the change needed is very simple:
Change
// hitting this exactly is like finding the proverbial needle
// in the haystack -- almost impossible to do.
if (current == disired)
to
// this is guaranteed to work.
// note if this is in English, you'll want to change disired to desired
if (current >= disired)
Having said this, your while (true) loop is not a good thing to do as it will needlessly tie up the CPU with empty cycles. Instead use some type of event notification or call-back system like ChangeListener or a PropertyChangeListener or a Timer.
You state:
yes it is within a swing GUI
You're calling a long while (true) block of code on the Swing event thread, rendering this thread ineffective. Since the event thread is responsible for all Swing graphics and user interactions, this effectively freezes your GUI until the while loop completes. The solution is obvious: 1) use a Swing Timer for your delay, not a while true loop (this is the callback mechanism that I mentioned in my original answer), and 2) in the future, please give us this important relevant information with the original question since it changes the entire nature of the question.
e.g.
// caveat: code not tested
System.out.println("System Exiting...");
int delay = 4 * 1000;
new Timer(delay, new ActionListener(){
#Override
public void actionPerformed(ActionEvent e) {
System.out. println("Exited");
System.exit(0);
}
}).start();
e.g.,
import java.awt.Component;
import java.awt.Window;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import javax.swing.*;
#SuppressWarnings("serial")
public class TestDelayedExit extends JPanel {
private static final int GAP = 100;
public TestDelayedExit() {
add(new JButton(new DisposeAction("Exit", KeyEvent.VK_X)));
setBorder(BorderFactory.createEmptyBorder(GAP, GAP, GAP, GAP));
}
private static void createAndShowGui() {
JFrame frame = new JFrame("TestDelayedExit");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(new TestDelayedExit());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
private class DisposeAction extends AbstractAction {
private int count = 4;
private Timer timer;
public DisposeAction(String name, int mnemonic) {
super(name);
putValue(MNEMONIC_KEY, mnemonic); // for alt-key combo
}
#Override
public void actionPerformed(ActionEvent e) {
if (timer != null && timer.isRunning()) {
return;
}
final Component c = (Component) e.getSource();
int timerDelay = 1000;
putValue(NAME, String.valueOf(count));
timer = new Timer(timerDelay, new ActionListener() {
public void actionPerformed(ActionEvent e) {
if (count == 0) {
((Timer) e.getSource()).stop();
// this will not work for JMenuItems, and for that
// you would need to get the pop up window's parent component
Window win = SwingUtilities.getWindowAncestor(c);
if (win != null) {
win.dispose();
}
} else {
count--;
putValue(NAME, String.valueOf(count));
}
}
});
timer.start();
}
}
}

Make method that returns when JButton is pressed

I need to make a method that returns only when a JButton is pressed. I have a custom JButton class
public class MyButton extends JButton {
public void waitForPress() {
//returns only when user presses this button
}
}
and I want to implement waitForPress. Basically, the method should only return when the user presses the button with their mouse. I have achieved similar behavior for JTextField (to return only when user presses Space):
public void waitForTriggerKey() {
final CountDownLatch latch = new CountDownLatch(1);
KeyEventDispatcher dispatcher = new KeyEventDispatcher() {
public boolean dispatchKeyEvent(KeyEvent e) {
if (e.getID() == KeyEvent.KEY_PRESSED && e.getKeyCode() == KeyEvent.VK_SPACE) {
System.out.println("presed!");
latch.countDown();
}
return false;
}
};
KeyboardFocusManager.getCurrentKeyboardFocusManager().addKeyEventDispatcher(dispatcher);
try {
//current thread waits here until countDown() is called (see a few lines above)
latch.await();
} catch (InterruptedException e1) {
e1.printStackTrace();
}
KeyboardFocusManager.getCurrentKeyboardFocusManager().removeKeyEventDispatcher(dispatcher);
}
but I would like to do the same thing with JButton.
In advance: Please, if you wish to comment saying that this is not a good idea and that one should simply wait for actionPerformed event on a JButton and then do some action, please realize I already know that and have a good reason for doing what I'm asking here. Please try to only help with what I've asked. Thanks!!
In advance: Please, also realize that implementing actionPerformed also will not directly solve the problem. Because the code will progress even without the button being pressed. I need the program to stop, and only return when the button has been pressed. Here is a terrible solution if I were to use actionPerformed:
public class MyButton extends JButton implements ActionPerformed {
private boolean keepGoing = true;
public MyButton(String s) {
super(s);
addActionListener(this);
}
public void waitForPress() {
while(keepGoing);
return;
}
public void actionPerformed(ActionEvent e) {
keepGoing = false;
}
}

For what it's worth, here is how you can do it with wait() and notify() but yet I feel that there is a deeper problem here. I would not consider this as a satisfying solution:
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;
public class TestBlockingButton {
boolean clicked = false;
private Object toNotify;
private void initUI() {
JFrame frame = new JFrame(TestBlockingButton.class.getSimpleName());
JButton button = new JButton("Click me");
button.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
clicked = true;
if (toNotify != null) {
synchronized (TestBlockingButton.this) {
toNotify.notify();
}
}
}
});
frame.add(button);
frame.setSize(400, 400);
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public void waitForProcess() {
toNotify = this;
while (!clicked) {
synchronized (this) {
try {
wait();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
System.out.println("continuing work");
}
public static void main(String[] args) {
final TestBlockingButton test = new TestBlockingButton();
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
test.initUI();
}
});
ScheduledExecutorService pool = Executors.newScheduledThreadPool(1);
pool.execute(new Runnable() {
#Override
public void run() {
System.out.println("I was doing something and now I will wait for button click");
test.waitForProcess();
System.out.println("User has now cliked the button and I can continue my work");
}
});
}
}

As you asked for an implementation with a mutex, here's what it would be like.
I'm using an ActionListener though, but there's no busy wait in it. If that isn't what you desire, you atleast saw what Burkhard meant ;)
public class MyButton extends JButton implements ActionListener
{
private Semaphore sem = new Semaphore(1);
public MyButton(String text) throws InterruptedException
{
super(text);
addActionListener(this);
sem.acquire();
}
#Override
public void actionPerformed(ActionEvent e) {
sem.release();
}
public void waitForPress() throws InterruptedException {
sem.acquire();
//do your stuff
sem.acquire();
//or just
//waitForPress()
//if you dont want it to end.
}
public static void main(String[] args) throws InterruptedException {
JFrame frame = new JFrame();
MyButton m = new MyButton("test");
frame.add(m);
frame.pack();
frame.setVisible(true);
m.waitForPress();
//another time, if you only want it to block twice
m.waitForPress();
}
}
But I don't think this is a clean approach, but it doesn't consume CPU-time like a while(isStatementTrue)-implementation.
An important thing here is: you're blocking the main thread with m.waitForPress() but as you wrote you're quite experienced and you know how to handle that.

JOptionPane.showMessageDialog wait until OK is clicked?

This might be a very simple thing that I'm overlooking, but I just can't seem to figure it out.
I have the following method that updates a JTable:
class TableModel extends AbstractTableModel {
public void updateTable() {
try {
// update table here
...
} catch (NullPointerException npe) {
isOpenDialog = true;
JOptionPane.showMessageDialog(null, "No active shares found on this IP!");
isOpenDialog = false;
}
}
}
However, I don't want isOpenDialog boolean to be set to false until the OK button on the message dialog is pressed, because if a user presses enter it will activate a KeyListener event on a textfield and it triggers that entire block of code again if it's set to false.
Part of the KeyListener code is shown below:
public class KeyReleased implements KeyListener {
...
#Override
public void keyReleased(KeyEvent ke) {
if(txtIPField.getText().matches(IPADDRESS_PATTERN)) {
validIP = true;
} else {
validIP = false;
}
if (ke.getKeyCode() == KeyEvent.VK_ENTER) {
if (validIP && !isOpenDialog) {
updateTable();
}
}
}
}
Does JOptionPane.showMessageDialog() have some sort of mechanism that prevents executing the next line until the OK button is pressed? Thank you.

The JOptionPane creates a modal dialog and so the line beyond it will by design not be called until the dialog has been dealt with (either one of the buttons have been pushed or the close menu button has been pressed).
More important, you shouldn't be using a KeyListener for this sort of thing. If you want to have a JTextField listen for press of the enter key, add an ActionListener to it.

An easy work around to suite your needs is the use of showConfirmDialog(...), over showMessageDialog(), this lets you take the input from the user and then proceed likewise. Do have a look at this example program, for clarification :-)
import javax.swing.*;
public class JOptionExample
{
public static void main(String... args)
{
SwingUtilities.invokeLater(new Runnable()
{
public void run()
{
int selection = JOptionPane.showConfirmDialog(
null
, "No active shares found on this IP!"
, "Selection : "
, JOptionPane.OK_CANCEL_OPTION
, JOptionPane.INFORMATION_MESSAGE);
System.out.println("I be written" +
" after you close, the JOptionPane");
if (selection == JOptionPane.OK_OPTION)
{
// Code to use when OK is PRESSED.
System.out.println("Selected Option is OK : " + selection);
}
else if (selection == JOptionPane.CANCEL_OPTION)
{
// Code to use when CANCEL is PRESSED.
System.out.println("Selected Option Is CANCEL : " + selection);
}
}
});
}
}

You can get acces to the OK button if you create optionpanel and custom dialog. Here's an example of this kind of implementation:
/*
* To change this template, choose Tools | Templates
* and open the template in the editor.
*/
/**
*
* #author OZBORN
*/
public class TestyDialog {
static JFrame okno;
static JPanel panel;
/**
* #param args the command line arguments
*/
public static void main(String[] args) {
zrobOkno();
JButton przycisk =new JButton("Dialog");
przycisk.setSize(200,200);
panel.add(przycisk,BorderLayout.CENTER);
panel.setCursor(null);
BufferedImage cursorImg = new BufferedImage(16, 16, BufferedImage.TYPE_INT_ARGB);
przycisk.setCursor(Toolkit.getDefaultToolkit().createCustomCursor(
cursorImg, new Point(0, 0), "blank cursor"));
final JOptionPane optionPane = new JOptionPane(
"U can close this dialog\n"
+ "by pressing ok button, close frame button or by clicking outside of the dialog box.\n"
+"Every time there will be action defined in the windowLostFocus function"
+ "Do you understand?",
JOptionPane.INFORMATION_MESSAGE,
JOptionPane.DEFAULT_OPTION);
System.out.println(optionPane.getComponentCount());
przycisk.addActionListener(new ActionListener(){
#Override
public void actionPerformed(ActionEvent e) {
final JFrame aa=new JFrame();
final JDialog dialog = new JDialog(aa,"Click a button",false);
((JButton)((JPanel)optionPane.getComponents()[1]).getComponent(0)).addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
aa.dispose();
}
});
dialog.setContentPane(optionPane);
dialog.pack();
dialog.addWindowFocusListener(new WindowFocusListener() {
#Override
public void windowLostFocus(WindowEvent e) {
System.out.println("Zamykam");
aa.dispose();
}
#Override public void windowGainedFocus(WindowEvent e) {}
});
dialog.setVisible(true);
}
});
}
public static void zrobOkno(){
okno=new JFrame("Testy okno");
okno.setLocationRelativeTo(null);
okno.setSize(200,200);
okno.setPreferredSize(new Dimension(200,200));
okno.setVisible(true);
okno.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
panel=new JPanel();
panel.setPreferredSize(new Dimension(200,200));
panel.setLayout(new BorderLayout());
okno.add(panel);
}
}

Try this,
catch(NullPointerException ex){
Thread t = new Thread(new Runnable(){
public void run(){
isOpenDialog = true;
JOptionPane.setMessageDialog(Title,Content);
}
});
t.start();
t.join(); // Join will make the thread wait for t to finish its run method, before
executing the below lines
isOpenDialog = false;
}

Java: How to continuously update JLabel which uses atomicInteger to countdown after ActionListener

I was reading different threads on the subject which suggested the Swing Timer class or SwingUtilities.InvokeLater
...but I am having a lot of trouble wrapping my head around them.
I used atomicInteger to create my countdown timer and it works fine in the console. However, When I try to incorporate it in Swing, it only updates the starting and ending value (e.g. set a 5 sec countdown will display in the frame: "5" -> after 5 seconds -> "0".
Is there any simple way for me to keep and "refresh" my atomicInteger countdown label, or the only way is using the Swing Timer class?
Thank you for your patience!
ps. not homework, just trying to make myself a custom timer to study. (ie. procrastinating)
I hope this class is enough, please let me know if you need the frame/panel code as well.
private class ClickListener implements ActionListener{
public void actionPerformed(ActionEvent e){
int t_study = 5;
atomicDown.set(t_study);
if (e.getSource() == b_study){
while(atomicDown.get() > 0){
t_study = atomicDown.decrementAndGet();
l_studyTime.setText(Integer.toString(t_study));
try {
Thread.sleep(1000);
}
catch (InterruptedException e1) {
System.out.println("ERROR: Thread.sleep()");
e1.printStackTrace();
}
}
}
else if(e.getSource() == b_exit){
System.exit(0);
}
else
System.out.println("ERROR: button troll");
}
}

After turning the code snippet into an SSCCE, this is what I get (which seems to work - as best as I understand the original code).
I have not changed the variable names. Please learn common Java naming conventions1 for class, method & attribute names & use it consistently.
Specifically names like b_study should be more along the lines of studyButton or similar. Some will note that 'button' should not be part of the name, but when you have a GUI with both a 'Study' button & label, I don't see any other logical way to separate them.
import java.awt.event.*;
import javax.swing.*;
import java.util.concurrent.atomic.AtomicInteger;
class TimerTicker {
public static final int STUDY_TIME = 15;
AtomicInteger atomicDown = new AtomicInteger(STUDY_TIME);
JButton b_study;
JButton b_exit;
JLabel l_studyTime;
TimerTicker() {
JPanel gui = new JPanel();
b_study = new JButton("Study");
ClickListener listener = new ClickListener();
b_study.addActionListener(listener);
gui.add(b_study);
b_exit = new JButton("Exit");
b_exit.addActionListener(listener);
gui.add(b_exit);
l_studyTime = new JLabel("" + atomicDown.get());
gui.add(l_studyTime);
JOptionPane.showMessageDialog(null, gui);
}
private class ClickListener implements ActionListener {
Timer timer;
public void actionPerformed(ActionEvent e){
if (e.getSource() == b_study) {
ActionListener countDown = new ActionListener() {
public void actionPerformed(ActionEvent ae) {
if (!(atomicDown.get() > 0)) {
timer.stop();
// reset the count.
atomicDown.set(STUDY_TIME);
} else {
l_studyTime.setText(
Integer.toString(
atomicDown.decrementAndGet()));
}
}
};
timer = new Timer(1000,countDown);
timer.start();
} else if(e.getSource() == b_exit) {
System.exit(0);
} else {
System.out.println("ERROR: button troll");
}
}
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
new TimerTicker();
}
});
}
}