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Java provides us ways to interrupt an executing thread. We can interrupt a java thread by calling interrupt() method on it. On the call to interrupt() method, a java thread will automatically throw an exception of type InterruptedException in a couple of situations.

Situations when a thread throws InterruptedException



• When a thread was interrupted by interrupt() method before an activity of waiting or sleeping.
• When a thread was interrupted by interrupt() method during an activity of waiting or sleeping.

Interrupting a thread while during it is sleeping -:

In this code, we are trying to make a thread throw an InterruptedException by calling interrupt() method on it, during its sleep(after calling sleep() method on it).

class Intr implements Runnable	   	    //implementing the Runnable interface
{

public void run()  //Entry Point of the new thread.
{

try
{
	Thread.sleep(3000); //This will make the thread(Thread2) sleep for 3000ms.
	
}
catch(InterruptedException e)
{
	System.out.println("Thread is interrupted - " + e);
}			

}


public static void main(String... ar)
{
Intr newTh= new Intr();
Thread th= new Thread(newTh, "Thread2");    //Calling Thread's constructor & passing the object
					    //of class that  implemented  Runnable interface
					    //& the name of new thread.

//Starts the thread(Thread2)
th.start();		

//Main thread interrupting the thread(Thread2) while it is sleeping, causing InterruptedException
th.interrupt();		
}

}

Output is - :

Thread is interrupted - java.lang.InterruptedException: sleep interrupted

Program Analysis

• In the main() method, we have created a new thread with the name, Thread2, pointed by th.
• Method call th.start() starts the Thread2, which starts executing its run() method.
• In run() method, sleep () method is called on the Thread2 to make it sleep for 3000 ms/3 seconds.
• While the Thread2 is sleeping, the main thread calls interrupt() on it, which interrupts its sleep and it throws an InterruptedException.

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Interrupting a thread while before it is sleeping -:

Now we are trying to make the main thread(default thread) throw an InterruptedException by calling interrupt() method on it, before it is going to sleep(by calling sleep() method).

class Intr 
{

public static void main(String... ar)
{	
//Accessing the reference of main thread, a default thread
Thread th = Thread.currentThread(); 

//Interrupting the main thread.
th.interrupt();

try
{
	Thread.sleep(3000);
}
catch(Exception e)
{
	System.out.println(e + " in "+ th.getName()); //Printing the name of main thread.
}

}
}

Output is :

java.lang.InterruptedException: sleep interrupted in main

Program Analysis

• We have obtained the reference of the main thread, which is a default thread.
• Method interrupt() is called on the main thread, which sets its interrupt flag to true. Now, the main thread throw InterruptedException if it calls wait(), sleep() or join() method in the upcoming code.
• As a result, Main thread throws InterruptedException as soon as sleep() method is called on it, hence, interrupting the sleep activity.
• InterruptedException thrown by the main thread is caught in the catch block & it prints thread name.

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