Java Programming - Threads

Exercise : Threads - General Questions
Which two of the following methods are defined in class Thread?
  1. start()
  2. wait()
  3. notify()
  4. run()
  5. terminate()
1 and 4
2 and 3
3 and 4
2 and 4
Answer: Option

(1) and (4). Only start() and run() are defined by the Thread class.

(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.

Which three guarantee that a thread will leave the running state?
  1. yield()
  2. wait()
  3. notify()
  4. notifyAll()
  5. sleep(1000)
  6. aLiveThread.join()
  7. Thread.killThread()
1, 2 and 4
2, 5 and 6
3, 4 and 7
4, 5 and 7
Answer: Option

(2) is correct because wait() always causes the current thread to go into the object's wait pool.

(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.

Which of the following will directly stop the execution of a Thread?
exits synchronized code
Answer: Option

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

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

Option C is wrong. notifyAll() - wakes up all threads that are waiting on this object's monitor.

Option D is wrong. Typically, releasing a lock means the thread holding the lock (in other words, the thread currently in the synchronized method) exits the synchronized method. At that point, the lock is free until some other thread enters a synchronized method on that object. Does entering/exiting synchronized code mean that the thread execution stops? Not necessarily because the thread can still run code that is not synchronized. I think the word directly in the question gives us a clue. Exiting synchronized code does not directly stop the execution of a thread.

Which method must be defined by a class implementing the java.lang.Runnable interface?
void run()
public void run()
public void start()
void run(int priority)
Answer: Option

Option B is correct because in an interface all methods are abstract by default therefore they must be overridden by the implementing class. The Runnable interface only contains 1 method, the void run() method therefore it must be implemented.

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.

Which will contain the body of the thread?
Answer: Option

Option A is Correct. The run() method to 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. The start() method causes this thread to begin execution; the Java Virtual Machine calls the run method of this thread.

Option C is wrong. The stop() method is deprecated. It forces the thread to stop executing.

Option D is wrong. Is the main entry point for an application.