Threads and Concurrency Quiz - Languages Java

Free practice quiz: Threads and Concurrency (Languages Java). 55 multiple-choice questions with answers and explanations. Play online, no sign-up needed.

This Languages Java practice quiz has 55 multiple-choice questions on Threads and Concurrency, and 55 of them come with an explanation. Try the 5 sample questions below (tap an option to check yourself), then play the full quiz online. No sign-up needed.

Sample questions

1. What is the primary mechanism by which Java achieves concurrency?

   1. Processes
   2. Threads
   3. Coroutines
   4. Asynchronous programming models
   Show answer

   Answer: B. Threads

   Java's concurrency model is built around the concept of threads, which are lightweight units of execution that can run concurrently within a single process.

2. Which exception is thrown by `Thread.sleep()`?

   1. IllegalThreadStateException
   2. InterruptedException
   3. ThreadDeath
   4. NullPointerException
   Show answer

   Answer: B. InterruptedException

   `Thread.sleep()` can be interrupted by another thread calling the `interrupt()` method on the sleeping thread. If this happens, `Thread.sleep()` throws an `InterruptedException`.

3. What is `ReentrantLock` in Java?

   1. A simple synchronization mechanism that is less flexible than `synchronized` blocks.
   2. A more flexible and powerful locking mechanism than `synchronized` keywords, allowing reentrant locking, fairness, and timed waits.
   3. A mechanism for creating daemon threads.
   4. A method to make threads sleep.
   Show answer

   Answer: B. A more flexible and powerful locking mechanism than `synchronized` keywords, allowing reentrant locking, fairness, and timed waits.

   `ReentrantLock` implements the `Lock` interface and provides explicit locking and unlocking. It offers features like reentrancy (a thread can acquire the same lock multiple times), fairness policies (optional), and timed lock acquisition, which are not available with the basic `synchronized` keyword.

4. What is the purpose of the `synchronized` block `synchronized(object)`?

   1. To synchronize on the `Class` object.
   2. To synchronize on a specific instance of an object.
   3. To synchronize on the current thread's stack.
   4. To make the method static.
   Show answer

   Answer: B. To synchronize on a specific instance of an object.

   When you use `synchronized(object)`, the thread acquires the intrinsic lock associated with the `object` instance. This allows for fine-grained synchronization, where different blocks of code might synchronize on different objects, enabling more concurrent access than synchronizing an entire method or static method.

5. What is a `Phaser` in Java's concurrency utilities?

   1. A synchronization mechanism for a variable number of parties that may arrive and depart dynamically at barrier points.
   2. A way to create a thread pool with a fixed number of threads.
   3. A lock that can be acquired by multiple threads simultaneously.
   4. A mechanism for signaling between threads.
   Show answer

   Answer: A. A synchronization mechanism for a variable number of parties that may arrive and depart dynamically at barrier points.

   `Phaser` is a more flexible synchronization barrier than `CyclicBarrier` because the number of parties (threads) can change dynamically. Parties register with the `Phaser`, wait at a barrier point, and then can optionally deregister. It's useful for coordinating threads in complex, dynamic workflows.

More questions in this quiz

Answers and explanations are in the full quiz.

1. Which method is used to start a thread in Java?
2. What is the difference between `Thread.sleep(milliseconds)` and `Object.wait()`?
3. What is the purpose of the `synchronized` keyword in Java?
4. What is a deadlock in multithreaded programming?
5. Which interface defines the contract for executing a command on some underlying thread?
6. What is the difference between `wait()`, `notify()`, and `notifyAll()`?
7. What is a race condition?
8. Which of the following is NOT a state of a Java Thread?
9. What is the role of the `volatile` keyword in Java?
10. What is the `ExecutorService` interface primarily used for?
11. What is the purpose of `Thread.yield()`?
12. What is the difference between `start()` and `run()` methods of a `Thread` class?
13. What is the `daemon` property of a thread?
14. What is the purpose of the `join()` method in Java threads?
15. What does the `interrupt()` method do to a thread?
16. Which class provides a framework for managing threads and scheduling tasks in a more flexible way than direct thread manipulation?
17. What is the purpose of a thread-safe class?
18. What is a `Callable` interface in Java concurrency?
19. What is the purpose of a `Future` object in Java concurrency?
20. Which of the following is an example of a thread-safe collection in Java's `java.util.concurrent` package?
21. What is the purpose of `Thread.currentThread().interrupt()`?
22. What is the primary advantage of using an `ExecutorService` over manually creating `Thread` objects?
23. What is the purpose of `synchronized(this)` in Java?
24. What is a `CountDownLatch`?
25. What is `synchronized` on a static method equivalent to?
26. What is a `Semaphore` in Java's concurrency utilities?
27. What is the purpose of the `CompletableFuture` class introduced in Java 8?
28. What is the `yield()` method guaranteed to do?
29. What is an `Atomic` operation in Java concurrency?
30. Which of the following is NOT a way to create a thread in Java?
31. What is the primary purpose of the `java.util.concurrent.locks` package?
32. What is a `CyclicBarrier` used for?
33. What happens if a thread calls `wait()` on an object, but no other thread calls `notify()` or `notifyAll()` on that same object?
34. What is the purpose of the `Thread.yield()` method in the context of thread scheduling?
35. Which method is used to check if a thread has been interrupted?
36. What is the purpose of the `synchronized` keyword when applied to a method?
37. What is a thread pool in the context of `ExecutorService`?
38. What does `notifyAll()` do?
39. What is the purpose of the `Thread.activeCount()` method?
40. What is the key difference between `sleep()` and `wait()` regarding locks?
41. What is the purpose of the `ReentrantReadWriteLock`?
42. What is the `ThreadLocal` class primarily used for?
43. What does `notify()` do?
44. What is the main purpose of `Executors.newFixedThreadPool(int nThreads)`?
45. What is the meaning of reentrancy in the context of `ReentrantLock` or `synchronized` methods?
46. What is the default behavior of a `Thread` when it's created and started in Java?
47. What is the purpose of `Thread.join(long millis)`?
48. What is an `Executor` framework in Java?
49. What is the role of a `ThreadFactory`?
50. What is the significance of the `finally` block in relation to `synchronized` blocks?

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