I am trying to create a simple java program that will run indefinitely and output a number every second. I believe my code here should do this; however, it stops after the variable i gets to either 2, 3 or 4. Randomly. Most of the time it hits 3. I do not think that the program stopping is based on i at all, but something i'm overlooking perhaps.
All this program needs to do is spit out the second count using a timer. I feel like my code might be a little over complicated so please let me know if i'm making it too hard.
package testing;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.SwingUtilities;
import javax.swing.Timer;
public class driver {
static int delay = 1000; //milliseconds
private Timer timer;
int i = 0;
public driver(){
ActionListener taskPerformer = new ActionListener() {
public void actionPerformed(ActionEvent evt) {
System.out.println(i);
i++;
}
};
timer = new Timer(delay, taskPerformer);
timer.setInitialDelay(0);
timer.start();
}
public static void main(String args[]){
SwingUtilities.invokeLater(new Runnable()
{
#Override
public void run()
{
new driver();
}
});
}
}
Everything is just right in your program, but one.
Your program starts (from main() obviously), which starts the timer, timer method initiates the process of displaying time/number every second, and after that, the main thread dies! resulting in completion of program execution.
So to avoid this you simply can keep main thread busy.
Here's the simplest way :
public static void main(String args[]){
SwingUtilities.invokeLater(new Runnable()
{
#Override
public void run()
{
driver d = new driver();
}
});
for(;;); // <-- **Check this out :D**
}
Related
So, I've been messing around with the Swing Timer in Java, trying to make a little time counter. However, the actionperformed method doesn't seem to react whenever I make a timer and let it run.
Here's my simplified UI class:
public class UI implements ActionListener {
private int value = 0;
Timer timer = new Timer(5,this);
#Override
public void actionPerformed(ActionEvent e) {
value++;
System.out.println(value);
}
public void start() {
timer.start();
}
}
And this is what my launcher looks like:
public class Launcher {
public static void main(String[] args) {
UI ui = new UI();
ui.start();
}
}
When I run the launcher, nothing happens. I do know he creates the UI and lets the timer start, but the timer doesn't seem to call the Actionperformed method.
I'm wondering why.
It should show the value +1 every interval of 5 (miliseconds?).
Thanks in advance!
Your program is exiting before the timer Thread has a chance to start. You should give a little time before exiting the main Thread to allow the timer Thread to keep running. Thread.sleep(100) after ui.start()should solve.
hey i can help you out... you should do the following ;
firstly import the following ;
import java.awt.event.ActionEvent ;
import java.awt.event.ActionListener ;
import javax.swing.Timer ;
then initialize the timer at the end of the form like this ;
public static void main(String args[]) {
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
new mainprogramme().setVisible(true);
}
});
}
private Timer timer ;
then after initializing the timer add a public class like following;
public class progress implements ActionListener {
public void actionPerformed(ActionEvent evt){
int n = 0 ;
if (n<100){
n++ ;
System.out.println(n) ;
}else{
timer.stop() ;
}
}
}
after you do this go to the j Frame>right click and select>Events>window>window Opened and type the following ;
private void formWindowOpened(java.awt.event.WindowEvent evt) {
timer = new Timer(100,new progress()) ;
and after you do all this take a button name it as anything and type the following in its void like following ;
timer.start();
AND THAT'S IT CODE IT AND THEN REPLY ME...
I'm trying to implement a timer using one thread and print it on a JButton using another thread.
my class for time is like this:
public class Time extends Thread
{
int counter = 0;
public String currentTime = new String();
public String printFormat(int second)
{
return String.format("%d:%d", second/60, second%60);
}
synchronized public void count(int minute) throws InterruptedException
{
minute *= 60;
while(minute >= 0)
{
wait(1000);
minute--;
currentTime = printFormat(minute);
System.out.println(currentTime);
}
}
and my main thread is like this:
button.setText(time.currentTime);
what is wrong with this piece of code?
"if you can explain it using java swing timer , I would appreciate that"
If you want to use a javax.swing.Timer do the following, it really simple.
The same way you set a ActionListener to a button, you do the same for the timer. Except instead of the button firing the event, it's fired by the timer, every duration period you set for it.
In the case of a clock like timer, you would set it to 1000,
indication do something every 1000 milliseconds.
In this particular
example, I just set the text of the button with a count value that I
increment by one every time the timer event is fired. Heres the Timer code
Timer timer = new Timer(1000, new ActionListener(){
public void actionPerformed(ActionEvent e) {
button.setText(String.valueOf(count));
count++;
}
});
timer.start();
As you can see it' pretty simple
You can run this example
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;
import javax.swing.Timer;
public class ButtonTimer {
private JButton button = new JButton(" ");
private int count = 1;
public ButtonTimer() {
Timer timer = new Timer(1000, new ActionListener(){
public void actionPerformed(ActionEvent e) {
button.setText(String.valueOf(count));
count++;
}
});
timer.start();
JFrame frame = new JFrame();
frame.add(button);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
new ButtonTimer();
}
});
}
}
If you want help trying to figure out your current code, consider posting a runnable program we can test out. So we can see where you're going wrong.
Here's a tutorial on Concurrency With Swing
I am still a beginner at Java so I have not learned much about threads and concurrency. However, I would like to be able to use the ScheduledThreadPoolExecutor as a timer because of the problems I am having with java.util.Timer and TimerTask. I am extremely interested in the creation of threads and know that I will be learning about them in a few weeks. However, if possible could someone give me a basic example on how to convert my current mini test program using util.timer to using a ScheduledThreadPoolExecutor?
I would like to complete this example ASAP so I don't have much time to learn about threads - no matter how much I would like to. Having said this please include anything you feel is important that a java beginner should know with regards to ScheduledThreadPoolExecutor.
Example program
I have made a quick small example to represent the problem I am having in a larger program. What this program should do is allow the user to press a button to start a counter. The user must then be able to stop and restart the counter when ever s/he wants. In the larger program it is vital that this counter remains equal so I have used the
scheduleAtFixRate()
method. It is also important that the initial delay is always the same (in this case 0).
The problem (as I am sure you will see) is that once the timer is cancelled it cannot be restarted - something that I hope the ScheduledThreadPoolExecutor will resolve.
code:
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.TimerTask;
import java.util.Timer;
public class Tester extends JFrame {
JButton push = new JButton("Push");
static JTextArea textOut = new JTextArea();
Timer timer = new Timer();
boolean pushed = false;
static int i = 1;
public Tester() {
super();
add(push, BorderLayout.NORTH);
add(textOut);
push.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
if (!pushed) {
timer.scheduleAtFixedRate(new Task(), 0, 1000);
pushed = true;
} else {
timer.cancel();
pushed = false;
}
}
});
}
static class Task extends TimerTask {
public void run() {
textOut.setText("" + i++);
}
}
public static void main(String[] args) {
Tester a = new Tester();
a.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
a.pack();
a.setVisible(true);
}
}
I use this class a lot for testing so there may be extra code (I think I removed it all).
Replace
Timer timer = new Timer();
with
ScheduledExecutorService service = Executors.newSingleThreadScheduledExecutor();
and
class Task extends TimerTask
with
class Task implements Runnable
and
timer.scheduleAtFixedRate(new Task(), 0, 1000);
with
service.scheduleAtFixedRate(new Task(), 0, 1000, TimeUnit.MILLISECONDS);
BTW You should not be attempting to update the GUI on another thread. Instead you have to add a task to the Swing GUI Thread to perform the task
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
textOut.setText("" + i++);
}
});
Why won't this work?
I would like it to print every second.
Thanks.
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.Timer;
public class test2 {
public static void main(String[] args) {
Timer timer = new Timer(1000, new ActionListener() {
public void actionPerformed(ActionEvent e) {
System.out.println("hello");
}
});
timer.start();
}
}
Your program terminates before the timer can run even once. When the main method is terminated the program terminates and all threads will also terminate. This includes your timer thread.
Try the following:
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.Timer;
public class test2 {
public static void main(String[] args) {
Timer timer = new Timer(1000, new ActionListener() {
public void actionPerformed(ActionEvent e) {
System.out.println("hello");
}
});
timer.start();
}
while (true) /* no operation */;
}
}
Probably the timer is started in a daemon thread, and immediately after starting it, the main thread finishes.
As soon as there are only daemon threads left, the JVM may/must terminate. So you need to keep the main thread alive. For testing purposes a simple Thread.sleep(10000); should do well.
There's nothing preventing your code from exiting immediately after the call to start. Add Thread.sleep(10000); after timer.start(); and you'll see the message printed.
Because your program will exit soon after main thread is finished, and since timer runs on a separate thread it won't have time to execute. Adding a Thead.Sleep call before main method end would execute your code.
You are using interface libraries (java.awt) to write console applications.
Try this:
public static void main(String[] args) throws Exception {
while(true){
Thread.sleep(1000);
System.out.println("hello");
}
}
Bellow is the code for the simplest GUI countdown. Can the same be done in a shorter and more elegant way with the usage of the Swing timer?
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.SwingUtilities;
public class CountdownNew {
static JLabel label;
// Method which defines the appearance of the window.
public static void showGUI() {
JFrame frame = new JFrame("Simple Countdown");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
label = new JLabel("Some Text");
frame.add(label);
frame.pack();
frame.setVisible(true);
}
// Define a new thread in which the countdown is counting down.
public static Thread counter = new Thread() {
public void run() {
for (int i=10; i>0; i=i-1) {
updateGUI(i,label);
try {Thread.sleep(1000);} catch(InterruptedException e) {};
}
}
};
// A method which updates GUI (sets a new value of JLabel).
private static void updateGUI(final int i, final JLabel label) {
SwingUtilities.invokeLater(
new Runnable() {
public void run() {
label.setText("You have " + i + " seconds.");
}
}
);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
showGUI();
counter.start();
}
});
}
}
Yes you SHOULD use a Swing Timer. You SHOULD NOT, use a util Timer and TimerTask.
When a Swing Timer fires the code is executed on the EDT which means you just need to invoke the label.setText() method.
When using the uitl Timer and TimerTask, the code DOES NOT execute on the EDT, which means you need to wrap your code in a SwingUtilities.invokeLater to make sure the code executes on the EDT.
And that is way using a Swing Timer is shorter and more elegant than your current approach, it simplifies the coding because to code is executed on the EDT.
You could make it a little more elegant by using Timer with an appropriate TimerTask.
Yes, use a timer. updateGUI would be the code for the timer task, but it will need some changes as you won't be able to pass in i for each call since you just get a run() method.