SCJP Java Threads and Concurrency 4

Question 1

What happens when you call `Thread.sleep(0)` in Java?

Accepted Answer

The thread yields the CPU to other threads of equal or higher priority

Answer

`Thread.sleep(0)` causes the current thread to yield the processor, allowing other threads of equal or higher priority to execute.

Question 2

Which method in the `Object` class causes the current thread to release its lock and wait until another thread calls `notify()` or `notifyAll()`?

Accepted Answer

wait()

Answer

`wait()` releases the object's monitor lock and suspends the thread until it is notified or interrupted.

Question 3

A thread is in the WAITING state. Which of the following can transition it back to the RUNNABLE state?

Accepted Answer

Another thread calling notify() on the object it is waiting on

Answer

A thread in WAITING state is moved to RUNNABLE when another thread calls `notify()` or `notifyAll()` on the object the waiting thread holds a lock on.

Question 4

What is the effect of declaring a variable as `volatile` in Java?

Accepted Answer

It ensures that changes to the variable are immediately visible to all threads

Answer

`volatile` ensures that every read of the variable reflects the most recently written value, preventing CPU cache inconsistencies between threads.

Question 5

Which of the following correctly describes a 'deadlock' in Java threading?

Accepted Answer

Two or more threads are each waiting for a lock held by the other, causing all to block forever

Answer

Deadlock occurs when two or more threads form a circular dependency on locks, each waiting for the other to release its lock.

SCJP - Sun Certified Java Programmer Practice Test

SCJP - Sun Certified Java Programmer Practice Test

SCJP Java Threads and Concurrency 4