Tutorial
Thread.sleep() in Java - Java Thread sleep
Introduction
The Java Thread.sleep() method can be used to pause the execution of the current thread for a specified time in milliseconds. The argument value for milliseconds cannot be negative. Otherwise, it throws IllegalArgumentException.
sleep(long millis, int nanos) is another method that can be used to pause the execution of the current thread for a specified number of milliseconds and nanoseconds. The allowed nanosecond values are between 0 and 999999.
In this article, you will learn about Java’s Thread.sleep().
How Thread.sleep Works
Thread.sleep() interacts with the thread scheduler to put the current thread in a wait state for a specified period of time. Once the wait time is over, the thread state is changed to a runnable state and waits for the CPU for further execution. The actual time that the current thread sleeps depends on the thread scheduler that is part of the operating system.
Java Thread.sleep important points
- It always pauses the current thread execution.
- The actual time the thread sleeps before waking up and starting execution depends on system timers and schedulers. For a quiet system, the actual time for sleep is near to the specified sleep time, but for a busy system, it will be a little bit longer.
Thread.sleep()doesn’t lose any monitors or lock the current thread it has acquired.- Any other thread can interrupt the current thread in sleep, and in such cases
InterruptedExceptionis thrown.
Java Thread.sleep Example
Here is an example program where Thread.sleep() is used to pause the main thread execution for 2 seconds (2000 milliseconds):
First, this code stores the current system time in milliseconds. Then it sleeps for 2000 milliseconds. Finally, this code prints out the new current system time minus the previous current system time:
OutputSleep time in ms = 2005
Notice that this difference is not precisely 2000 milliseconds. This is due to how Thread.sleep() works and the operating system-specific implementation of the thread scheduler.
Conclusion
In this article, you learned about Java’s Thread.sleep().
Continue your learning with more Java tutorials.
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Thanks for short and useful post on Thread.sleep() method. I think 2000 is meant, and not 200, here: “If you will run the above program, you will notice that the sleep time it prints is slightly greater than 200 and caused by …” in this post. Please amend this.
- Rishi Raj
Please respond to my comment. It concerns readers.
- Rishi Raj
Thanku for short and useful notes on thread.sleep()…
- Balwant
hi sir just one question, once the thread is in sleep mode how can it be interrupted? You have mentioned this in 4 point as “Any other thread can interrupt the current thread in sleep, in that case InterruptedException is thrown.” thanks ashish
- Ashish
All sleep does is that it puts the thread into a “State” where it’s execution is “Suspended” i.e. it’s waiting. But it is still very much functional and has a “Waiting” state. The thread is also very much “Alive”. In this state, if you interrupt this thread, you are actually interrupting it’s current state i.e. “Waiting” state. From there, it will do the duties set within the “catch” block for InterruptedException being caught in the run() method.
- Mohammed Manna
still i didn’t get the answer for the question “once the thread is in sleep mode how can it be interrupted?”
- Sanjay
package com.org.multithreading.sleep; public class SleepInterupt { public static void main(String[] args) throws InterruptedException { Thread t = new InterruptDemo(); t.start(); t.interrupt(); } } class InterruptDemo extends Thread { public void run() { System.out.println(“Thread started…”); try { Thread.sleep(2000); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println(“Thread stopped…”); } }
- Sujit Lole
How to check whether thread is sleeping mode or not?
- Sundara Baskaran
class TestCallRun extends Thread{ public void run(){ for(int i=1;i<5;i++){ try{Thread.sleep(5000);}catch(InterruptedException e){System.out.println(e);} System.out.println(i); } } public static void main(String args[]){ TestCallRun2 t1=new TestCallRun2(); TestCallRun2 t2=new TestCallRun2(); t1.start(); t2.run(); } } why the output of above program is same as when we call t1.start(); t2.start(). 1 1 2 2 3 3 4 4 but output is different when we call t1.run();t2.run(); 1 2 3 4 1 2 3 4 according to my understating output of t1.start(); t2.run() should be 1 --t1 thread 1 --t2 thread 2 --t2 thread 3 --t2 thread 4 --t2 thread 2 --t1 thread 3 --t1 thread 4 --t1 thread
- Nitin
Although output of multi-threaded program depends on JVM, in this case output is correct. when you are using t1.start() and t2start() there are total of three threads in execution t1 t2 and main main completes its execution without printing anything. whereas t1 and t2 take turns, when of them is put to sleep other one kicks and complete some part of its execution. In second case there are two threads of execution one is t1 and other is main now t2.run is just a method in main which puts the current thread i.e., main to sleep and let t1 take turn. That’s the reason of your answer. If you want to observe this: create named threads and print their name along with integers in output.
- Vikas
Hi Pankaj, Your blog is very good and more informative. But its very good if you provide link to export to pdf. Thanks Maruthi
- maruthi
Hi Pankaj, I modified your code like below, and I can see same sleep time after every execution – long sleepTime = 999; System.out.println("Going to sleep for "+sleepTime); long start = 0L; try { start = System.currentTimeMillis(); Thread.sleep(sleepTime); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("Sleep time in ms = "+(System.currentTimeMillis()-start)); I guess, the difference is coming due to the startTime capture statement execution and the actual sleep statement, if you keep them one after the other, you won’t see the difference anymore. I understand that your explanation is correct too, because all thread execution depends on how OS allow them. Thanks
- Punit
Hi, I’m noticed your post.In your code,the result is same what you have said,I guess the reason for you got this result is you didn’t get the current time more precisely.Because CPU is very fast ,only you can see the difference when you use the System.nanoTime() to get the current time.Then you will see the print time is greater than the sleep time in nano second level. Let me know if you have any question about my answer. hope that helps.
- Banjamin
Thread One = new Thread( ()-> {}); What is the difference between calling One.sleep() and Thread.sleep();
- James
sleep is a static method hence we can call using instance as well, it will have same effect as calling Thread.sleep(). Recommended way to use static methods is using class name instead of instances.
- Bala
long start = System.currentTimeMillis(); what does this line have in the code?
- FREDY ORLANDO MARCELO CASTIBLANCO
i think that
- lily
System.out.println("Sleep time in ms = "+(System.currentTimeMillis()-start)); We are measuring current time minus time before we are putting the thread to sleep. So, we are checking how much time did the thread actually slept
- Praveen E
Suppose if a thread is kept in sleep and after completing sleep mode time the processor is running another thread. then will the current thread stops and executes thread that completed sleep mode or thread that is in sleep mode executed after current running process is terminated please explain it in detail I am new to java
- Pavan
how do we come to know that, how much time we have to provide to the threads for sleep or wait. If we are working on big projects.
- Ishant
how the execution of two threads goes when sleep is not there? how does thread scheduler perform in this case…?
- Swapna
without sleep it will print 0
- venkat
what is difference between t1.run() and t1.start()?
- Shweta
if you want the method to start in a new thread, you have to call start(). Otherwise you are still just running the code in the same thread.
- Lallos
the major difference between t1.run() and t1.start() is when you use t1.start() it means you start a thread… and t1.run() means you call a run() method only not a thread…
- Prashant Mishra
Sir can you please explain this topic { waiting of child thread until completing main thread}
- Pradeep Singh