Question 1

What will be the output of the program?

class MyThread extends Thread 
{
    MyThread() 
    {
        System.out.print(" MyThread");
    }
    public void run() 
    {
        System.out.print(" bar");
    }
    public void run(String s) 
    {
        System.out.println(" baz");
    }
}
public class TestThreads 
{
    public static void main (String [] args) 
    {
        Thread t = new MyThread() 
        {
            public void run() 
            {
                System.out.println(" foo");
            }
        };
        t.start();
    }
}

Answer

Answer: B

Option B is correct because in the first line of main we're constructing an instance of an anonymous inner class extending from MyThread. So the MyThread constructor runs and prints "MyThread". The next statement in main invokes start() on the new thread instance, which causes the overridden run() method (the run() method defined in the anonymous inner class) to be invoked, which prints "foo"

Question 2

public class MyRunnable implements Runnable 
{
    public void run() 
    {
        // some code here
    }
}

which of these will create and start this thread?

Answer

Answer: C

Because the class implements Runnable, an instance of it has to be passed to the Thread constructor, and then the instance of the Thread has to be started.

A is incorrect. There is no constructor like this for Runnable because Runnable is an interface, and it is illegal to pass a class or interface name to any constructor.

B is incorrect for the same reason; you can't pass a class or interface name to any constructor.

D is incorrect because MyRunnable doesn't have a start() method, and the only start() method that can start a thread of execution is the start() in the Thread class.

Question 3

Which class or interface defines the wait(), notify(),and notifyAll() methods?

Answer

Answer: A

The Object class defines these thread-specific methods.

Option B, C, and D are incorrect because they do not define these methods. And yes, the Java API does define a class called Class, though you do not need to know it for the exam.

Question 4

Which of the following will not directly cause a thread to stop?

Answer

Answer: A

Option A is correct. notify() - wakes up a single thread that is waiting on this object's monitor.

Option B is wrong. wait() causes the current thread to wait until another thread invokes the notify() method or the notifyAll() method for this object.

Option C is wrong. Methods of the InputStream class block until input data is available, the end of the stream is detected, or an exception is thrown. Blocking means that a thread may stop until certain conditions are met.

Option D is wrong. sleep() - Causes the currently executing thread to sleep (temporarily cease execution) for a specified number of milliseconds. The thread does not lose ownership of any monitors.

Question 5

Assume the following method is properly synchronized and called from a thread A on an object B:

wait(2000);

After calling this method, when will the thread A become a candidate to get another turn at the CPU?

Answer

Answer: A

Option A. Either of the two events (notification or wait time expiration) will make the thread become a candidate for running again.

Option B is incorrect because a waiting thread will not return to runnable when the lock is released, unless a notification occurs.

Option C is incorrect because the thread will become a candidate immediately after notification, not two seconds afterwards.

Option D is also incorrect because a thread will not come out of a waiting pool just because a lock has been released.

Questions for: Threads