Develop Reference

Making thread.sleep accurate

I am attempting to make a game loop that has an accurate timer. I know that TimeUnit uses thread.sleep(); which can vary by milliseconds. My question is simple:
Does this code make thread.sleep(); more accurate?
and further
Is there anything I can do to fix/make it better, or should I abandon it?
import java.util.concurrent.TimeUnit;
public class Timer implements Runnable {
public static void main(String[]args){
new Timer().start();
}
public int ups = 1;
#Override
public void run() {
int uc = 0;
long startTime = 0;
long result = 0;
long offset = 0;
while(true){
startTime = System.nanoTime();
uc++;
if(uc==1000/ups){
update();
uc=0;
}
result = System.nanoTime()-startTime;
if(1000000-result>0)
try {
int prefered = 1000000;
startTime = System.nanoTime();
TimeUnit.NANOSECONDS.sleep(prefered-result-offset);
offset = System.nanoTime()-startTime-prefered+result+offset;
} catch (InterruptedException e) {
System.out.println("an error has occured");
}
}
}
public void update(){
System.out.println("Hello World");
}
public void start(){
new Thread(this).start();
}
}
I have already seen this by the way. I might as well add
How does this compare to the other loop?
Edit: This is for a desktop game, not mobile

In case of games, I doubt you really want nanosecond precision in waking up. What you do want though is avoiding accumulating error, which is what your code is trying to do. It's a reasonable approach, although it probably would make more sense to use a Timer instead:
Timer timer = new Timer()
timer.scheduleAtFixedRate(new TimerTask() {
#Override
public void run() {
// Your periodic code here
}
}, 0, 1);

Run java function every hour

I want to run a function every hour, to email users a hourly screenshot of their progress. I code set up to do so in a function called sendScreenshot()
How can I run this timer in the background to call the function sendScreenshot() every hour, while the rest of the program is running?
Here is my code:
public int onLoop() throws Exception{
if(getLocalPlayer().getHealth() == 0){
playerHasDied();
}
return Calculations.random(200, 300);
}
public void sendScreenShot() throws Exception{
Robot robot = new Robot();
BufferedImage screenshot = robot.createScreenCapture(new Rectangle(Toolkit.getDefaultToolkit().getScreenSize()));
screenshotNumber = getNewestScreenshot();
fileName = new File("C:/Users/%username%/Dreambot/Screenshots/Screenshot" + screenshotNumber +".");
ImageIO.write(screenshot, "JPEG", fileName);
mail.setSubject("Your hourly progress on account " + accName);
mail.setBody("Here is your hourly progress report on account " + accName +". Progress is attached in this mail.");
mail.addAttachment(fileName.toString());
mail.setTo(reciepents);
mail.send();
}

Use a ScheduledExecutorService:
ScheduledExecutorService ses = Executors.newSingleThreadScheduledExecutor();
ses.scheduleAtFixedRate(new Runnable() {
#Override
public void run() {
sendScreenShot();
}
}, 0, 1, TimeUnit.HOURS);
Prefer using a ScheduledExecutorService over Timer:
Java Timer vs ExecutorService?

According to this article by Oracle, it's also possible to use the #Schedule annotation:
#Schedule(hour = "*")
public void doSomething() {
System.out.println("hello world");
}
For example, seconds and minutes can have values 0-59, hours 0-23, months 1-12.
Further options are also described there.

java's Timer works fine here.
http://docs.oracle.com/javase/6/docs/api/java/util/Timer.html
Timer t = new Timer();
t.scheduleAtFixedRate(new TimerTask() {
public void run() {
// ...
}
}, delay, 1 * 3600 * 1000); // 1 hour between calls

For this type of period execution, meaning every day or every hour, all you need is using a Timer like this :
public static void main(String[] args) throws InterruptedException {
Calendar today = Calendar.getInstance();
today.set(Calendar.HOUR_OF_DAY, 7);
today.set(Calendar.MINUTE, 45);
today.set(Calendar.SECOND, 0);
Timer timer = new Timer();
TimerTask task = new TimerTask() {
#Override
public void run() {
System.out.println("I am the timer");
}
};
// timer.schedule(task, today.getTime(), TimeUnit.MILLISECONDS.convert(1, TimeUnit.DAYS)); // period: 1 day
timer.schedule(task, today.getTime(), TimeUnit.MILLISECONDS.convert(5, TimeUnit.SECONDS)); // period: 5 seconds
}
this exemple will execute the timetask every 5 seconds from the current date and 7:45 am.
Good Luck.

while (true) {
DateTime d = new DateTime();
switch(d.getMinuteOfHour()) {
case 56:
runHourly();
break;
case 41:
if(d.getHourOfDay() == 2) {
runAt0241Daily();
}
break;
}
SUM.wait(59000);
}
How about this for something you can control and understand?

Android CountDownTimer Class Lagging Main Thread

I am trying to use android.os.CountDownTimer to literally show a countdown timer via a textview for fitness purposes. The issue I am having is the timer seems to be having trouble running on the main thread i.e. the countdown will jump 2-4 secs and is clearly being "lagged" - the timer is intended to be in an endless loop until a stop button is pressed.
I am new to Java and Android and cannot figure out how to get the countdown timer running and updating the UI without any conflicts or lagging.
I have attempted to put the CountDown in a Handler/Runnable and an Asynctask with no luck.
MainActivity
CountDownTimer timer;
void countdownTimer() {
long min = countdownMins * 60000;
long sec = countdownSecs * 1000;
long milliseconds = min+sec;
timer = null;
timer = new CountDownTimer(milliseconds, 1000) {
public void onTick(long millisUntilFinished) {
long mins = millisUntilFinished / 60000;
long secs = millisUntilFinished % 60000 / 1000;
String display = String.format("%02d:%02d", mins, secs);
tvTextView.setText(display);
}
public void onFinish() {
countdownTimer();
}
}.start();
}
Many thanks to anyone who can show me how to get this running off the main thread so my UI elements will be smooth.

I decided to take a different approach which has served my purposes very well. No lag or thread issues and can easily be restarted over and over. Hope this helps someone out.
int startCountdown = 5;
int currentCountdown;
Handler countdownHandler = new Handler();
Timer countdownTimer = new Timer();
public void startCountdownTimer() {
currentCountdown = startCountdown;
for (int i = 0; i <= startCountdown; i++) {
TimerTask task = new TimerTask() {
#Override
public void run() {
countdownHandler.post(doA);
}
};
countdownTimer.schedule(task, i * 1000);
}
}
final Runnable doA = new Runnable() {
#Override
public void run() {
if (currentCountdown != 0) {
tvTextView.setText("" + currentCountdown);
currentCountdown--;
} else {
currentCountdown = startCountdown;
startCountdownTimer();
}
}
};

Try to use Handler and runnable instead of CountDownTimer. Here is a good article about this approach
http://www.mopri.de/2010/timertask-bad-do-it-the-android-way-use-a-handler/
One more thing you could try is
void countdownTimer() {
final Runnable runnable = new Runnable() {
#Override
public void run() {
tvTextView.setText(display);
}
};
long min = countdownMins * 60000;
long sec = countdownSecs * 1000;
long milliseconds = min + sec;
timer = null;
timer = new CountDownTimer(milliseconds, 1000) {
public void onTick(long millisUntilFinished) {
long mins = millisUntilFinished / 60000;
long secs = millisUntilFinished % 60000 / 1000;
final String display = String.format("%02d:%02d", mins, secs);
textView.post(runnable);
}
public void onFinish() {
countdownTimer();
}
}.start();
}

If you countdown with changing your TextView fast and frequently. You have to set your TextView width and height in a fix number, or it will lag while calculating your view scale.

Making a program run for 5 minutes

So I wanted to try out something for a bit with the Timer and TimerTask classes.
I was able to get a line of code to execute after 30 seconds elapsed.
What I've been trying to do now is to get this line of code to execute for 5 minuets.
This is what I originally tried
public static void main(String[] args)
{
for ( int i = 0; i <= 10; i ++ )
{
Timer timer = new Timer();
timer.schedule( new TimerTask()
{
public void run()
{
System.out.println("30 Seconds Later");
}
}, 30000
);
}
}
I used the number 10 in the for loop to see if the timer.schedule would wait for another 30 seconds during the next iteration of the loop.
Any idea how I should go about this? I tried using the schedule method with a parameter passed in for period, but that only made it re-execute and it never stopped.

Java has provided a rich set of APIs in java.util.concurrent package to achieve such tasks. One of these APIs is ScheduledExecutorService. For example consider the code given below: This code will execute the Runnable task after every 30 seconds for upto 5 minutes:
import java.util.concurrent.*;
class Scheduler
{
private final ScheduledExecutorService service;
private final long period = 30;//Repeat interval
public Scheduler()
{
service = Executors.newScheduledThreadPool(1);
}
public void startScheduler(Runnable runnable)
{
final ScheduledFuture<?> handler = service.scheduleAtFixedRate(runnable,0,period,TimeUnit.SECONDS);//Will cause the task to execute after every 30 seconds
Runnable cancel = new Runnable()
{
#Override
public void run()
{
handler.cancel(true);
System.out.println("5 minutes over...Task is cancelled : "+handler.isCancelled());
}
};
service.schedule(cancel,5,TimeUnit.MINUTES);//Cancels the task after 5 minutes
}
public static void main(String st[])
{
Runnable task = new Runnable()//The task that you want to run
{
#Override
public void run()
{
System.out.println("I am a task");
}
};
Scheduler sc = new Scheduler();
sc.startScheduler(task);
}
}

The issue you're running into is that the scheduled Timer runs on a different thread - that is, the next iteration of your for loop starts running immediately after scheduling, not 30 seconds later. It looks like your code starts ten timers all at once, which means they should all print (roughly) 30 seconds later, all at once.
You were on the right track when you tried using the recurring version of schedule (with the third parameter). As you noted, this isn't quite what you want because it runs indefinitely. However, Timer does have a cancel method to prevent subsequent executions.
So, you should try something like:
final Timer timer = new Timer();
// Note that timer has been declared final, to allow use in anon. class below
timer.schedule( new TimerTask()
{
private int i = 10;
public void run()
{
System.out.println("30 Seconds Later");
if (--i < 1) timer.cancel(); // Count down ten times, then cancel
}
}, 30000, 30000 //Note the second argument for repetition
);

here's a workaround I'm ashamed of presenting:
package test;
import java.util.Date;
import java.util.Timer;
import java.util.TimerTask;
public class FiveMinutes {
private static int count = 0;
// main method just to add example
public static void main(String[] args) {
Timer timer = new Timer();
timer.schedule(new TimerTask() {
#Override
public void run() {
System.out.println("Count is: " + count);
if (count == 1) {
System.err.println("... quitting");
System.exit(0);
}
count++;
}
},
// starting now
new Date(),
// 5 minutes
300000l
);
}
}
Also please note that the application might not run exactly 5 minutes - see documentation for TimerTask.

Your solution is pretty close to working, you just have to multiply the delay by the counter (in your case, i):
public static void main(String[] args)
{
for (int i = 1; i <= 10; i++) // start i at 1 for initial delay
{
Timer timer = new Timer();
timer.schedule(new TimerTask() {
public void run()
{
System.out.println("30 Seconds Later");
}
}, 30000 * i); // 5 second intervals
}
}

I don't know if this solution has problems with the garbage collector or not, but I throw it in here anyways. Maybe someone clears that out, and I learn something as well. Basically a timer sets a new timer if there is time left, and it should stop after 5 minutes.
Main.java:
public class Main {
public static void main(String[] args) {
MyTimer myTimer = new MyTimer(300000,30000);
myTimer.startTimer();
}
}
MyTimer.java:
import java.util.Timer;
import java.util.TimerTask;
public class MyTimer {
private int totalRunningTime;
private int currentTime = 0;
private int intervalTime;
private Timer timer = new Timer();
public MyTimer(int totalRunningTime, int intervalTime) {
this.totalRunningTime = totalRunningTime;
this.intervalTime = intervalTime;
}
public void startTimer() {
startTimer(intervalTime);
}
private void startTimer(int time) {
timer.schedule(new TimerTask() {
public void run() {
if (currentTime <= totalRunningTime - intervalTime) {
printTimeSinceLast(intervalTime / 1000);
currentTime += intervalTime;
startTimer(intervalTime);
} else if (currentTime < totalRunningTime) {
int newRestIntervalTime = totalRunningTime - currentTime;
printTimeSinceLast(newRestIntervalTime / 1000);
currentTime += newRestIntervalTime;
startTimer(newRestIntervalTime);
}
}
}, time);
}
private void printTimeSinceLast(int timeSinceLast) {
System.out.println(timeSinceLast + " seconds later.");
}
}

Java - Countdown timer without GUI

Basically I am making a text based "game" (Not so much a game, more of a way to improve basic java skills and logic). However, as part of it I wish to have a timer. It would count down on the time I wish from the variable to 0. Now, I have seen a few ways to do this with a gui, however, is there a way to do this without a gui/jframe etc.
So, what I am wondering is. Can you make a count down from x to 0 without using a gui/jframe. If so, how would you go about this?
Thanks, once I have some ideas will edit with progress.
Edit
// Start timer
Runnable r = new TimerEg(gameLength);
new Thread(r).start();
Above is how I am calling the thread/timer
public static void main(int count) {
If I then have this in the TimerEg class, the timer complies. However, when compiling the main in the other thread I get.
Now, am I completely miss-understanding threads and how this would work? Or is there something I am missing?
Error:
constructor TimerEg in class TimerEg cannot be applied to given types;
required: no arguments; found int; reason: actual and formal arguments differ in length
Found on line Runnable r = new TimerEg(gameLength);

Same as with a GUI, you'd use a Timer, but here instead of using a Swing Timer, you'd use a java.util.Timer. Have a look at the Timer API for the details. Also have a look at the TimerTask API since you would use this in conjunction with your Timer.
For example:
import java.util.Timer;
import java.util.TimerTask;
public class TimerEg {
private static TimerTask myTask = null;
public static void main(String[] args) {
Timer timer = new Timer("My Timer", false);
int count = 10;
myTask = new MyTimerTask(count, new Runnable() {
public void run() {
System.exit(0);
}
});
long delay = 1000L;
timer.scheduleAtFixedRate(myTask, delay, delay);
}
}
class MyTimerTask extends TimerTask {
private int count;
private Runnable doWhenDone;
public MyTimerTask(int count, Runnable doWhenDone) {
this.count = count;
this.doWhenDone = doWhenDone;
}
#Override
public void run() {
count--;
System.out.println("Count is: " + count);
if (count == 0) {
cancel();
doWhenDone.run();
}
}
}

You could write your own countdown timer, as simply as:
public class CountDown {
//Counts down from x to 0 in approximately
//(little more than) s * x seconds.
static void countDown(int x, int s) {
while (x > 0 ) {
System.out.println("x = " + x);
try {
Thread.sleep(s*1000);
} catch (Exception e) {}
x--;
}
}
public static void main(String[] args) {
countDown(5, 1);
}
}
Or you could use Java Timer API

It is simple to countdown with java..
int minute=10,second=60; // 10 min countdown
int delay = 1000; //milliseconds
ActionListener taskPerformer = new ActionListener() {
public void actionPerformed(ActionEvent evt) {
second--;
// do something with second and minute. put them where you want.
if (second==0) {
second=59;
minute--;
if (minute<0) {
minute=9;
}
}
}
};
new Timer(delay, taskPerformer).start();