I'm solving an exercise for my university and there is this code in my pdf that my supposed to use to delay the change of the colour of the text on a button, i don't understand how it exactly works so please can someone explain it
HandlerThread handlerThread = new HandlerThread("showText");
handlerThread.start();
Handler handler = new Handler(handlerThread.getLooper());
Runnable runnable = new Runnable() {
int i = 0;
#Override
public void run() {
i++;
handler.postDelayed(this, 1000);
if (i > 1)
button.setTextColor(getResources().getColor(android.R.color.transparent));
}
};
handler.post(runnable);
This code is in obscure way causing that Runnable to be called with the delay of 1s (every second) because it reschedules itself each time. The int i is guarding button.setTextColor from executing the first the.
This code is however very messy, the way it should be done is as follows:
Runnable runnable = new Runnable() {
#Override
public void run() {
button.setTextColor(getResources().getColor(android.R.color.transparent));
}
};
handler.postDelayed(runnable, 1000);
or with lambda expression just as following:
handler.postDelayed(() -> button.setTextColor(getResources().getColor(android.R.color.transparent)), 1000);
I'm currently programming a mini game in java swing. I've got the GUI set up, and the game involves a sequence of numbers flashing up on screen and then disappearing - the user must then input the numbers again in the sequence they appeared.
When the numbers are initially displayed, I want them to display for 1-2 seconds, and then disappear, and have another number for 1-2 seconds etc.
However, I'm having issues with delaying the program whilst the number displays. I can't use Thread.sleep as it pauses the whole program with the hiding of previous numbers etc. It just doesn't work. I've tried every other suggestion I've come across, none of which have worked yet.
Anyone got anymore tips?
int delay = 5000; // delay in milliseconds
ActionListener taskPerformer = new ActionListener() {
public void actionPerformed(ActionEvent evt) { //...Perform a task... } };
Timer timer = new Timer(delay, taskPerformer);
timer.setRepeats(false);
timer.start(); // timer starts - after delay time your task gets executed
Source
You can use Thread.sleep()
The problem you having is probably because you are trying to update the UI from Swing's event dispatching thread. This is a thread that is reserved for Swing components and you should do exactly nothing in it except quick updates to the UI.
public void prog() {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
label.setText("1");
}
}
try {
Thread.sleep(5000);
} catch(Exception e) { }
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
label.setText("2");
}
}
}
public static void main(String[] args) {
label = new JLabel("0");
prog();
}
JLabel label
The UI should remain responsive because of it's component interactions should be implemented in ActionListener's. But if you want to perform other work while waiting, or if the feature is contained in an ActionListener's actionPerfomed() method, you can kick off a new thread to sleep 5 seconds then update the UI. You could also perform some calculations that take 5 seconds to compute instead of sleeping without blocking the UI. The code would be:
(new Thread(new Runnable() {
#Override
public void run() {
try {
Thread.sleep(5000);
} catch (Exception e) { }
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
label.setText("2");
}
}
}
}).start();
I am having trouble delaying the method assign_backgrounds() within a for loop. I am trying to create a Simon says game, but instead of delaying and showing the next button that "Simon" presses, it shows all the buttons at once. Any help here would be greatly appreciated. Thanks.
boolean simonsTurn = true;
int x = 4;
int s;
int delay = 1000;
int array_values[] = new int[]{1,2,3,4};
public void simonSays() {
// running = true;
if (simonsTurn == true) {
go();
for (int i = 0; i < x; i++) {
Handler handler = new Handler();
handler.postDelayed(new Runnable() {
public void run() {
go();
}
}, 1000);
}
}
}
public void go(){
s = random_int_between(0,3);
assign_backgrounds(array_values[s]);
}
public void assign_backgrounds( int array_values ){
Handler handler = new Handler();
if( array_values == 1){
button1_.invalidate();
button1_.setBackgroundResource(R.drawable.goatclicked);
button1_.refreshDrawableState();
handler.postDelayed(new Runnable(){
public void run(){
button1_.invalidate();
button1_.setBackgroundResource(R.drawable.goat);
button1_.refreshDrawableState();}}, 1000);
}
else if( array_values == 2){
button2_.invalidate();
button2_.setBackgroundResource(R.drawable.pigclicked);
button2_.refreshDrawableState();
handler.postDelayed(new Runnable(){
public void run(){
button2_.invalidate();
button2_.setBackgroundResource(R.drawable.pig);
button2_.refreshDrawableState();}}, 1000);
}
else if( array_values == 3){
button3_.invalidate();
button3_.setBackgroundResource(R.drawable.chickenclicked);
button3_.refreshDrawableState();
handler.postDelayed(new Runnable() {
public void run() {
button3_.invalidate();
button3_.setBackgroundResource(R.drawable.chicken);
button3_.refreshDrawableState();}}, 1000);
}
if( array_values == 4) {
button4_.invalidate();
button4_.setBackgroundResource(R.drawable.cowclicked);
button4_.refreshDrawableState();
handler.postDelayed(new Runnable(){
public void run(){
button4_.invalidate();
button4_.setBackgroundResource(R.drawable.cow);
button4_.refreshDrawableState();}}, 1000);
}
}
It's because you are creating handlers very fast and then they are all starting at the same time. You should look into how Handler's work and about Asyncronous/Background tasks.
Now back to your problem, you are calling the a loop and it is creating handlers all in a row and they are being created very fast (nanoseconds). They will then all launch 1 second from that creation time because of your postDelayed() call. This is why everything is popping up at the same time! All of these delay posts are being executed at almost the same time on concurrent background threads.
Instead of a for(int i,...) loop you want to have a global int i, just add it to the top of the file.
At the end of any of Simon's turn you'll want, inside of the if, else if statement inside assign_background (at the end of the Runnables, then you'll want to call go().
This might cause problems because you are trying to access the main thread from all these background threads. so you might have to call the function runOnMainUIThread() as a quick hack when you call the go function.
All in all, you are going to have some problems until you understand Handlers, Background Processes, and Threads. Definitely great knowledge to learn about and Android has solid documentation on it just FYI.
private class MultipleGensListener implements ActionListener
{
public void actionPerformed(ActionEvent e)
{
for(int i = 0; i < 25; i++)
{
game.runSimulationOneGen();
changeGrid();
}
}
}
//this is the loop. The changeGrid method displays a game grid on a GUI but
// only the 25th iteration is visible on screen. I would like each one to be
// visible for about a half a second before the loop continues.
// I have seen some questions answered on here that are very close to what I'm asking,
// but I just don't really understand how to apply it to my program..
// thanks for any help.
If the code performed by the simulation is quick and does not consume too much CPU and time, then consider using a Swing Timer to do your looping and delay. Otherwise, you'll need to use a background thread such as can be done with a SwingWorker object.
For e.g. if using both Swing Timer and SwingWorker:
private class MultipleGensListener implements ActionListener {
protected static final int MAX_INDEX = 25;
public void actionPerformed(ActionEvent e) {
int timerDelay = 500; // ms delay
new Timer(timerDelay, new ActionListener() {
int index = 0;
public void actionPerformed(ActionEvent e) {
if (index < MAX_INDEX) { // loop only MAX_INDEX times
index++;
// create the SwingWorker and execute it
new SwingWorker<Void, Void>() {
#Override
protected Void doInBackground() throws Exception {
game.runSimulationOneGen(); // this is done in background thread.
return null;
}
#Override
protected void done() {
changeGrid(); // this is called on EDT after background thread done.
}
}.execute(); // execute the SwingWorker
} else {
((Timer) e.getSource()).stop(); // stop the timer
}
}
}).start(); // start the Swing timer
}
}
NEVER BLOCK THE GUI EVENT THREAD
you can use a timer for that and have it only fire 25 times
final Timer t = new Timer(500,null);
t.addActionListener(new ActionListener(){
int i=0;
public void actionPerformed(ActionEvent e){
game.runSimulationOneGen();//run 1 iteration per tick
changeGrid();
if(i>25){t.stop();}
i++;
}
});
t.setRepeats(true);
t.start();
btw the reason only the last iteration is shown is that gui updates (redraws) are done in a separate event, but to let another event trigger you need to return from the listener method which you didn't
the Timer I showed is a more elaborate iteration which lets other events run in between iterations allowing the gui to show the changes
check my post that shows both methods java.swing.Timer#setDelay(int)
and
correct usage of Thread.sleep(int)
java wait cursor display problem
I have a specific function that I want to be executed after 5 seconds.
How can I do that in Java?
I found javax.swing.timer, but I can't really understand how to use it. It looks like I'm looking for something way simpler then this class provides.
Please add a simple usage example.
new java.util.Timer().schedule(
new java.util.TimerTask() {
#Override
public void run() {
// your code here
}
},
5000
);
EDIT:
javadoc says:
After the last live reference to a Timer object goes away and all outstanding tasks have completed execution, the timer's task execution thread terminates gracefully (and becomes subject to garbage collection). However, this can take arbitrarily long to occur.
Something like this:
// When your program starts up
ScheduledExecutorService executor = Executors.newSingleThreadScheduledExecutor();
// then, when you want to schedule a task
Runnable task = ....
executor.schedule(task, 5, TimeUnit.SECONDS);
// and finally, when your program wants to exit
executor.shutdown();
There are various other factory methods on Executor which you can use instead, if you want more threads in the pool.
And remember, it's important to shutdown the executor when you've finished. The shutdown() method will cleanly shut down the thread pool when the last task has completed, and will block until this happens. shutdownNow() will terminate the thread pool immediately.
Example of using javax.swing.Timer
Timer timer = new Timer(3000, new ActionListener() {
#Override
public void actionPerformed(ActionEvent arg0) {
// Code to be executed
}
});
timer.setRepeats(false); // Only execute once
timer.start(); // Go go go!
This code will only be executed once, and the execution happens in 3000 ms (3 seconds).
As camickr mentions, you should lookup "How to Use Swing Timers" for a short introduction.
As a variation of #tangens answer: if you can't wait for the garbage collector to clean up your thread, cancel the timer at the end of your run method.
Timer t = new java.util.Timer();
t.schedule(
new java.util.TimerTask() {
#Override
public void run() {
// your code here
// close the thread
t.cancel();
}
},
5000
);
My code is as follows:
new java.util.Timer().schedule(
new java.util.TimerTask() {
#Override
public void run() {
// your code here, and if you have to refresh UI put this code:
runOnUiThread(new Runnable() {
public void run() {
//your code
}
});
}
},
5000
);
Your original question mentions the "Swing Timer". If in fact your question is related to SWing, then you should be using the Swing Timer and NOT the util.Timer.
Read the section from the Swing tutorial on "How to Use Timers" for more information.
you could use the Thread.Sleep() function
Thread.sleep(4000);
myfunction();
Your function will execute after 4 seconds. However this might pause the entire program...
ScheduledThreadPoolExecutor has this ability, but it's quite heavyweight.
Timer also has this ability but opens several thread even if used only once.
Here's a simple implementation with a test (signature close to Android's Handler.postDelayed()):
public class JavaUtil {
public static void postDelayed(final Runnable runnable, final long delayMillis) {
final long requested = System.currentTimeMillis();
new Thread(new Runnable() {
#Override
public void run() {
// The while is just to ignore interruption.
while (true) {
try {
long leftToSleep = requested + delayMillis - System.currentTimeMillis();
if (leftToSleep > 0) {
Thread.sleep(leftToSleep);
}
break;
} catch (InterruptedException ignored) {
}
}
runnable.run();
}
}).start();
}
}
Test:
#Test
public void testRunsOnlyOnce() throws InterruptedException {
long delay = 100;
int num = 0;
final AtomicInteger numAtomic = new AtomicInteger(num);
JavaUtil.postDelayed(new Runnable() {
#Override
public void run() {
numAtomic.incrementAndGet();
}
}, delay);
Assert.assertEquals(num, numAtomic.get());
Thread.sleep(delay + 10);
Assert.assertEquals(num + 1, numAtomic.get());
Thread.sleep(delay * 2);
Assert.assertEquals(num + 1, numAtomic.get());
}
All other unswers require to run your code inside a new thread.
In some simple use cases you may just want to wait a bit and continue execution within the same thread/flow.
Code below demonstrates that technique. Keep in mind this is similar to what java.util.Timer does under the hood but more lightweight.
import java.util.concurrent.TimeUnit;
public class DelaySample {
public static void main(String[] args) {
DelayUtil d = new DelayUtil();
System.out.println("started:"+ new Date());
d.delay(500);
System.out.println("half second after:"+ new Date());
d.delay(1, TimeUnit.MINUTES);
System.out.println("1 minute after:"+ new Date());
}
}
DelayUtil Implementation
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;
public class DelayUtil {
/**
* Delays the current thread execution.
* The thread loses ownership of any monitors.
* Quits immediately if the thread is interrupted
*
* #param duration the time duration in milliseconds
*/
public void delay(final long durationInMillis) {
delay(durationInMillis, TimeUnit.MILLISECONDS);
}
/**
* #param duration the time duration in the given {#code sourceUnit}
* #param unit
*/
public void delay(final long duration, final TimeUnit unit) {
long currentTime = System.currentTimeMillis();
long deadline = currentTime+unit.toMillis(duration);
ReentrantLock lock = new ReentrantLock();
Condition waitCondition = lock.newCondition();
while ((deadline-currentTime)>0) {
try {
lock.lockInterruptibly();
waitCondition.await(deadline-currentTime, TimeUnit.MILLISECONDS);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
return;
} finally {
lock.unlock();
}
currentTime = System.currentTimeMillis();
}
}
}
public static Timer t;
public synchronized void startPollingTimer() {
if (t == null) {
TimerTask task = new TimerTask() {
#Override
public void run() {
//Do your work
}
};
t = new Timer();
t.scheduleAtFixedRate(task, 0, 1000);
}
}
I think in this case :
import javax.swing.*;
import java.awt.event.ActionListener;
is the best. When the Question is prevent Ui stack or a progress not visible before a heavy work or network call. We can use the following methods (from my experience) :
Run a method after one Second :
public static void startMethodAfterOneSeconds(Runnable runnable) {
Timer timer = new Timer(1000, new ActionListener() {
#Override
public void actionPerformed(java.awt.event.ActionEvent e) {
runnable.run();
}
});
timer.setRepeats(false); // Only execute once
timer.start();
}
Run a method after n second once, Non repeating :
public static void startMethodAfterNMilliseconds(Runnable runnable, int milliSeconds) {
Timer timer = new Timer(milliSeconds, new ActionListener() {
#Override
public void actionPerformed(java.awt.event.ActionEvent e) {
runnable.run();
}
});
timer.setRepeats(false); // Only execute once
timer.start();
}
Run a method after n seconds, and repeat :
public static void repeatMethodAfterNMilliseconds(Runnable runnable, int milliSeconds) {
Timer timer = new Timer(milliSeconds, new ActionListener() {
#Override
public void actionPerformed(java.awt.event.ActionEvent e) {
runnable.run();
}
});
timer.setRepeats(true); // Only execute once
timer.start();
}
And the Usage :
startMethodAfterNMilliseconds(new Runnable() {
#Override
public void run() {
// myMethod(); // Your method goes here.
}
}, 1000);
Perhaps the most transparent way is to use the postDelayed function of the Handler class the following way:
new Handler().postDelayed(this::function, 1000);
or you can implement the function inside, for example:
new Handler().postDelayed(() -> System.out.println("A second later"), 1000);
Where the first argument is the function, the second argument is the delay time in milliseconds.
In the first example, the name of the called function is "function".