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The Java Interview Handbook: 300+ Interview Questions

Volatile

Explore the role of the volatile keyword in Java multi-threading to ensure that updates to a variable are visible across threads. Learn why volatile can prevent unpredictable behavior without requiring synchronization when a variable is read by one thread and written by another.

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1.

Explain the concept of volatile

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Technical Quiz
1.

Consider the class setup below:

class TaleOfTwoThreads {

    boolean flag = true;

    public void signalToStop() {
        flag = false;
    }


    public void run() {

        while (flag) {

            // ... Run like crazy
        }
    }
}

When will the “All Done” statement be printed for the following snippet

        TaleOfTwoThreads example = new TaleOfTwoThreads();

        // start runner thread
        Thread runner = new Thread(() -> example.run());
        runner.start();

        // wait for one second before signalling to stop
        Thread.sleep(1000);
        Thread stopper = new Thread(() -> example.signalToStop());
        stopper.start();

        // wait for two threads to complete processing
        stopper.join();
        runner.join();
        System.out.println("All Done");
A.

Printed roughly after one second

B.

Exception thrown because we aren’t synchronizing access to flag

C.

Never printed

D.

May be printed after atleast one second

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