Make a thread sleep :sleep()

Causes the currently executing thread to sleep (temporarily cease execution) for the specified number of time

A sleeping thread does not use any processor cycles because its execution is suspended for the specified duration.

Thread API provides 2 Methods to make a thread to sleep

public static void sleep(long millis) throws InterruptedException

public static void sleep(long millis, int nanos) throws InterruptedException

sleep method throws InterruptedExceiption, If a sleeping thread interrupted , it throws Interrupted Exception. Will see more details in the Interrupts section.

public static void sleep(long millis) throws InterruptedException

Causes the currently executing thread to sleep (temporarily cease execution) for the specified number of milliseconds, subject to the precision and accuracy of system timers and schedulers. The thread does not lose ownership of any monitors. Will discuss about acquiring abut monitor in synchronization topic

public static void sleep(long millis, int nanos) throws InterruptedException

Causes the currently executing thread to sleep (cease execution) for the specified number of milliseconds plus the specified number of nanoseconds. The thread does not lose ownership of any monitors. Better don't depend on nano seconds, they are depend on the underlying system Architecture.

sleep is a static method, so we have to call by class name.

You must handle the Interrupted Exception, otherwise compiler will throw error.

Example

class MyThread implements Runnable{
 public void run(){
  System.out.println("About to call sleep method");
  Thread.sleep(1000);
  System.out.println("sleep time finished");
 }

 public static void main(String args[]){
  MyThread task = new MyThread();
  Thread t1 = new Thread(task);
  t1.start();
 }
}

When you try to compile, you will get the compile time error

MyThread.java:5: error: unreported exception InterruptedException; must be caught or declared to be thrown
Thread.sleep(1000);
^
1 error

To make the above program run, handle the exception

class MyThread implements Runnable{

 public void run(){
  System.out.println("About to call sleep method");
  try{
   Thread.sleep(1000);
  }
  catch(InterruptedException e){
  }
  System.out.println("sleep time finished");
 }

 public static void main(String args[]){
  MyThread task = new MyThread();
  Thread t1 = new Thread(task);
  t1.start();
 }
}

     

Output

About to call sleep method
sleep time finished

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