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Interrupting a Thread:

If any thread is in sleeping or waiting state (i.e. sleep() or wait() is invoked), calling the interrupt() method on the thread, breaks out the sleeping or waiting state throwing InterruptedException. If the thread is not in the sleeping or waiting state, calling the interrupt() method performs normal behaviour and doesn't interrupt the thread but sets the interrupt flag to true. Let's first see the methods provided by the Thread class for thread interruption.

The 3 methods provided by the Thread class for interrupting a thread

  • public void interrupt()
  • public static boolean interrupted()
  • public boolean isInterrupted()

Example of interrupting a thread that stops working

In this example, after interrupting the thread, we are propagating it, so it will stop working. If we don't want to stop the thread, we can handle it where sleep() or wait() method is invoked. Let's first see the example where we are propagating the exception.
Test it Now
Output:Exception in thread-0  
       java.lang.RuntimeException: Thread interrupted...
       java.lang.InterruptedException: sleep interrupted
       at A.run(A.java:7)

Example of interrupting a thread that doesn't stop working

In this example, after interrupting the thread, we handle the exception, so it will break out the sleeping but will not stop working.
Test it Now
Output:Exception handled  
       java.lang.InterruptedException: sleep interrupted
       thread is running...

Example of interrupting thread that behaves normally

If thread is not in sleeping or waiting state, calling the interrupt() method sets the interrupted flag to true that can be used to stop the thread by the java programmer later.
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Output:1
       2
       3
       4 
       5

What about isInterrupted and interrupted method?

The isInterrupted() method returns the interrupted flag either true or false. The static interrupted() method returns the interrupted flag afterthat it sets the flag to false if it is true.
Test it Now
Output:Code for interrupted thread
       code for normal thread
       code for normal thread
       code for normal thread
       




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