In this example we will discuss about InterruptedException in Java. This exception is thrown when a thread is interrupted. The thread could be in either waiting, sleeping or running state and this exception can be thrown either before or during a thread’s activity.
This exception extends the Exception class and thus, can be classified as a checked exception. Checked exceptions must be explicitly declared in a method’s or constructor’s throw clause.
Finally, the InterruptedException exists since the 1.0 version of Java.
The Structure of InterruptedException
Constructors
InterruptedException()InterruptedException(String s)
Creates an instance of the InterruptedException class, setting null as its message.
Creates an instance of the InterruptedException class, using the specified string as message. The string argument indicates the name of the class that threw the error.
The InterruptedException in Java
A sample example where a thread is being interrupted is shown below:
SampleThread.java:
import java.util.concurrent.TimeUnit;
public class SampleThread extends Thread {
public SampleThread() {
super();
System.out.println("An instance of the " + SampleThread.class + " class was created!");
}
@Override
public void run() {
try {
/* Sleep for some seconds. */
TimeUnit.SECONDS.sleep(10);
}
catch(InterruptedException ex) {
System.err.println("An InterruptedException was caught: " + ex.getMessage());
}
}
}
First, we define the SampleThread class, which extends the Thread class and overrides its run method.
InterruptedExceptionExample.java:
public class InterruptedExceptionExample {
public static void main(String[] args) throws InterruptedException {
// Create a new thread.
Thread thread = new SampleThread();
//Start the thread's execution.
thread.start();
//Interrupt the thread.
thread.interrupt();
//Join the thread.
thread.join();
}
}
Then, we create an instance of the SampleThread and interrupt it during its execution. A sample execution is shown below:
An instance of the class main.java.SampleThread class was created! An InterruptedException was caught: sleep interrupted
More about the InterruptedException in Java
As we already mentioned, every thread has a boolean flag that represents its interrupted status. Initially, this status is set to false for every thread. If a thread is interrupted during an interruptible method such as join or sleep, it will unblock and throw an InterruptedException. In any other case, the thread’s interruption will only update the thread’s interrupted status. A thread can test if its interrupted using one of the following methods:
Notice that the 2nd method does not affect the interrupted status of the thread, in contrast to the 1st method which clears the interrupted status of the calling thread. A second call to the Thread::interrupted() method returns false, unless the calling thread was interrupted again.
How to deal with the InterruptedException
- The most simple strategy is to throw the
InterruptedExceptionto the upper layer of the calling stack and let the upper layer handle it. - Another strategy is to catch the
InterruptedException, perform some memory cleanup and then, propagate the exception to the upper layer of the calling stack. - Moreover, for those cases where a method cannot throw an
InterruptedException, you can use the following method, in order to interrupt the current thread:
Thread.currentThread().interrupt();
This approach can be very useful, because once a Thread catches an InterruptedException, its interrupted status is cleared and instead of ignoring the exception, we restore the interrupted status of the current Thread.
InterruptedException.Download the Eclipse Project
The Eclipse project of this example: InterruptedExceptionExample.zip.
This was a tutorial about InterruptedException in Java.
