Threads problems
- 1. Which three are methods of the Object class?
- notify();
- notifyAll();
- isInterrupted();
- synchronized();
- interrupt();
- wait(long msecs);
- sleep(long msecs);
- yield();
Options- A. 1, 2, 4
- B. 2, 4, 5
- C. 1, 2, 6
- D. 2, 3, 4 Discuss
Correct Answer: 1, 2, 6
Explanation:
(3), (5), (7), and (8) are incorrect answers. The methods isInterrupted() and interrupt() are instance methods of Thread.
The methods sleep() and yield() are static methods of Thread.
D is incorrect because synchronized is a keyword and the synchronized() construct is part of the Java language.
- 2. Which of the following line of code is suitable to start a thread?
class X implements Runnable { public static void main(String args[]) { /* Missing code? */ } public void run() {} }
Options- A. Thread t = new Thread(X);
- B. Thread t = new Thread(X); t.start();
- C. X run = new X(); Thread t = new Thread(run); t.start();
- D. Thread t = new Thread(); x.run(); Discuss
Correct Answer: X run = new X(); Thread t = new Thread(run); t.start();
Explanation:
Option C is suitable to start a thread.
- 3. Which three guarantee that a thread will leave the running state?
- yield()
- wait()
- notify()
- notifyAll()
- sleep(1000)
- aLiveThread.join()
- Thread.killThread()
Options- A. 1, 2 and 4
- B. 2, 5 and 6
- C. 3, 4 and 7
- D. 4, 5 and 7 Discuss
Correct Answer: 2, 5 and 6
Explanation:
(5) is correct because sleep() will always pause the currently running thread for at least the duration specified in the sleep argument (unless an interrupted exception is thrown).
(6) is correct because, assuming that the thread you're calling join() on is alive, the thread calling join() will immediately block until the thread you're calling join() on is no longer alive.
(1) is wrong, but tempting. The yield() method is not guaranteed to cause a thread to leave the running state, although if there are runnable threads of the same priority as the currently running thread, then the current thread will probably leave the running state.
(3) and (4) are incorrect because they don't cause the thread invoking them to leave the running state.
(7) is wrong because there's no such method.
- 4. Which two are valid constructors for Thread?
- Thread(Runnable r, String name)
- Thread()
- Thread(int priority)
- Thread(Runnable r, ThreadGroup g)
- Thread(Runnable r, int priority)
Options- A. 1 and 3
- B. 2 and 4
- C. 1 and 2
- D. 2 and 5 Discuss
Correct Answer: 1 and 2
Explanation:
(3), (4), and (5) are not legal Thread constructors, although (4) is close. If you reverse the arguments in (4), you'd have a valid constructor.
- 5. Which cannot directly cause a thread to stop executing?
Options- A. Calling the SetPriority() method on a Thread object.
- B. Calling the wait() method on an object.
- C. Calling notify() method on an object.
- D. Calling read() method on an InputStream object. Discuss
Correct Answer: Calling notify() method on an object.
Explanation:
- 6. Which two of the following methods are defined in class Thread?
- start()
- wait()
- notify()
- run()
- terminate()
Options- A. 1 and 4
- B. 2 and 3
- C. 3 and 4
- D. 2 and 4 Discuss
Correct Answer: 1 and 4
Explanation:
(2) and (3) are incorrect because they are methods of the Object class. (5) is incorrect because there's no such method in any thread-related class.
- 7. Which method registers a thread in a thread scheduler?
Options- A. run();
- B. construct();
- C. start();
- D. register(); Discuss
Correct Answer: start();
Explanation:
Option A is wrong. The run() method of a thread is like the main() method to an application. Starting the thread causes the object's run method to be called in that separately executing thread.
Option B is wrong. There is no construct() method in the Thread class.
Option D is wrong. There is no register() method in the Thread class.
- 8. Which method must be defined by a class implementing the java.lang.Runnable interface?
Options- A. void run()
- B. public void run()
- C. public void start()
- D. void run(int priority) Discuss
Correct Answer: public void run()
Explanation:
Option A and D are incorrect because they are narrowing the access privileges i.e. package(default) access is narrower than public access.
Option C is not method in the Runnable interface therefore it is incorrect.
- 9. Which of the following will not directly cause a thread to stop?
Options- A. notify()
- B. wait()
- C. InputStream access
- D. sleep() Discuss
Correct Answer: notify()
Explanation:
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.
- 10. Which class or interface defines the wait(), notify(),and notifyAll() methods?
Options- A. Object
- B. Thread
- C. Runnable
- D. Class Discuss
Correct Answer: Object
Explanation:
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.
Programming
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