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This section includes InterviewSolutions, each offering curated multiple-choice questions to sharpen your knowledge and support exam preparation. Choose a topic below to get started.

1.

Under which conditions will a currently executing thread stop?

Answer» The statements (2) and (4) makes currently executing thread to stop.
Discussion
2.

Which method registers a thread in a thread scheduler?

Answer» Option C is correct. The start() method causes this thread to begin execution; the Java Virtual Machine calls the run method of this thread. 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.
Discussion
3.

Which three guarantee that a thread will leave the running state?

Answer» (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.
Discussion
4.

Which method must be defined by a class implementing the interface?

Answer» 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.
Discussion
5.

Which will contain the body of the thread?

Answer» 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.
Discussion
6.

Which two can be used to create a new Thread?

Answer» There are two ways of creating a thread; extend (sub-class) the Thread class and implement the Runnable interface. For both of these ways you must implement (override and not overload) the public void run() method. (1) is correct - Extending the Thread class and overriding its run method is a valid procedure. (4) is correct - You must implement interfaces, and runnable is an interface and you must also include the run method. (2) is wrong - Runnable is an interface which implements not Extends. Gives the error: (No interface expected here) (3) is wrong - You cannot implement java.lang.Thread (This is a Class). (Implements Thread, gives the error: Interface expected). Implements expects an interface. (5) is wrong - You cannot implement java.lang.Thread (This is a class). You Extend classes, and Implement interfaces. (Implements Thread, gives the error: Interface expected)
Discussion
7.

Which two statements are true?

Answer» Statements (4) and (6) are correct. (4) is correct because the wait() method is overloaded to accept a wait duration in milliseconds. If the thread has not been notified by the time the wait duration has elapsed, then the thread will move back to runnable even without having been notified. (6) is correct because wait()/notify()/notifyAll() must all be called from within a synchronized, context. A thread must own the lock on the object its invoking wait()/notify()/notifyAll() on. (1) is incorrect because wait()/notify() will not prevent deadlock. (2) is incorrect because a sleeping thread will return to runnable when it wakes up, but it might not necessarily resume execution right away. To resume executing, the newly awakened thread must still be moved from runnable to running by the scheduler. (3) is incorrect because synchronization prevents two or more threads from accessing the same object. (5) is incorrect because notify() is not overloaded to accept a duration.
Discussion
8.

the static method returns a reference to the currently executing object. What is the result of this code?

Answer» D. The sleep() method must be enclosed in a try/catch block, or the method printAll() must declare it throws the InterruptedException. A is incorrect, but it would be correct if the InterruptedException was dealt with. B is incorrect, but it would still be incorrect if the InterruptedException was dealt with because all Java code, including the main() method, runs in threads. C is incorrect. The sleep() method is static, so even if it is called on an instance, it still always affects the currently executing thread.
Discussion
9.

What will be the output of the program? and assuming that data must be protected from corruption, what—if anything—can you add to the preceding code to ensure the integrity of data?

Answer» Option D is correct because synchronizing the code that actually does the increase will protect the code from being accessed by more than one thread at a time. Option A is incorrect because synchronizing the run() method would stop other threads from running the run() method (a bad idea) but still would not prevent other threads with other runnables from accessing the increase() method. Option B is incorrect for virtually the same reason as A—synchronizing the code that calls the increase() method does not prevent other code from calling the increase() method.
Discussion
10.

Which class or interface defines the , ,and methods?

Answer» 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.
Discussion
11.

which of these will create and start this thread?

Answer» 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.
Discussion
12.

What is the name of the method used to start a thread execution?

Answer» Option B is Correct. The start() method causes this thread to begin execution; the Java Virtual Machine calls the run method of this thread. Option A is wrong. There is no init() method in the Thread class. Option C 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 D is wrong. The resume() method is deprecated. It resumes a suspended thread.
Discussion
13.

Which two are valid constructors for Thread?

Answer» (1) and (2) are both valid constructors for Thread. (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.
Discussion
14.

Which three are methods of the Object class?

Answer» (1), (2), and (6) are correct. They are all related to the list of threads waiting on the specified object. (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.
Discussion
15.

Which cannot directly cause a thread to stop executing?

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