SCJP Java Threads and Concurrency 2

Question 1

What does the `volatile` keyword guarantee for a variable in Java?

Accepted Answer

Visibility — all threads see the most recent write to the variable

Answer

`volatile` ensures that reads and writes to a variable go directly to main memory, guaranteeing visibility of changes across threads.

Question 2

Which method is used to start a thread's execution in Java?

Accepted Answer

start()

Answer

Calling `start()` on a `Thread` object creates a new OS thread and schedules the `run()` method for execution.

Question 3

What is a race condition in Java concurrency?

Accepted Answer

Unpredictable behavior caused by multiple threads accessing shared data without proper synchronization

Answer

A race condition occurs when the program's outcome depends on the non-deterministic ordering of unsynchronized thread operations.

Question 4

Which Java class provides a thread-safe, atomic integer that supports compound operations like increment?

Accepted Answer

AtomicInteger

Answer

`AtomicInteger` in `java.util.concurrent.atomic` provides atomic compound operations like `incrementAndGet()` without explicit synchronization.

Question 5

In Java, which method pair is used for inter-thread communication?

Accepted Answer

notify() and wait()

Answer

`wait()` and `notify()` (with `notifyAll()`) on an `Object` are used for coordinating thread communication through a shared monitor.

SCJP - Sun Certified Java Programmer Practice Test