Mastering Java: The Ultimate Quiz for 'Thinking in Java'

What is a semaphore?

1. A signaling mechanism

2. A data structure for concurrency

3. A type of exception

4. A memory management feature

The correct answer is: A signaling mechanism

A semaphore is a signaling mechanism used in computer science to control access to a shared resource between multiple threads or processes. This is done by using counters and the "wait" and "signal" operations. Option B, a data structure for concurrency, is incorrect because a semaphore itself is not a data structure, but rather uses data structures to function. Option C, a type of exception, is incorrect because a semaphore is not an error or exception, but rather a tool used to prevent potential errors. Option D, a memory management feature, is incorrect because a semaphore does not manage memory, but rather controls access to shared resources.