Question 1

What is the `AtomicInteger` class?

Accepted Answer

The `AtomicInteger` class provides thread-safe operations on an integer without locks, using low-level CPU instructions. Methods like `incrementAndGet()` ensure atomic updates—perfect for counters in multi-threaded apps without the overhead of `synchronized`.

Question 2

What is the `CyclicBarrier` class?

Accepted Answer

The `CyclicBarrier` makes a group of threads wait until all reach a common point, then releases them—reusable unlike `CountDownLatch`. It’s like a team huddle—everyone waits, then proceeds together—ideal for parallel tasks.

Question 3

What is a Java thread pool?

Accepted Answer

A thread pool manages a set of reusable threads to execute tasks, avoiding the overhead of creating new threads repeatedly. The `ExecutorService` framework provides implementations like `ThreadPoolExecutor`. It’s efficient for apps with many short-lived tasks—like web servers.

Question 4

What are Java Streams?

Accepted Answer

Java Streams, added in Java 8, let you process collections functionally with operations like filter, map, and reduce. They’re lazy—nothing happens until a terminal operation like `collect()` triggers them—and can run in parallel for performance. They make code cleaner but take practice to master.

Question 5

What is the `Class` class in Java?

Accepted Answer

The `Class` class represents a class or interface at runtime—think of it as metadata about a type. You get it via `.class` syntax or `getClass()`, and it’s used in reflection to inspect or instantiate objects dynamically. It’s the backbone of Java’s reflective abilities.

Question 6

What is a deadlock in Java?

Accepted Answer

A deadlock occurs when two or more threads are stuck, each waiting for a resource the other holds, so none can proceed. It’s a concurrency nightmare—like two people refusing to let go of locked doors. Avoid it with proper lock ordering or timeouts.

Question 7

What is the `BlockingQueue` interface?

Accepted Answer

The `BlockingQueue` interface (from `java.util.concurrent`) is a queue that blocks when adding to a full queue or removing from an empty one—perfect for producer-consumer patterns. Implementations like `ArrayBlockingQueue` handle thread coordination smoothly.

Question 8

What is the difference between `HashMap` and `ConcurrentHashMap`?

Accepted Answer

Both are key-value stores, but `HashMap` is not thread-safe and faster for single-threaded use, while `ConcurrentHashMap` is designed for multithreading with better performance than `Hashtable`. It allows concurrent reads and updates by segmenting the map—great for high-concurrency apps.

Question 9

What is the `Future` interface?

Accepted Answer

The `Future` interface represents the result of an asynchronous task—like a promise of a value to come. You get it from `ExecutorService.submit()`, and methods like `get()` block until the result’s ready. It’s key for managing background tasks.

Question 10

What is the `ExecutorService` in Java?

Accepted Answer

The `ExecutorService` is an interface for managing threads, typically via thread pools. It abstracts thread creation and task execution with methods like `submit()` and `shutdown()`. It’s a high-level concurrency tool—think of it as a thread manager for busy apps.

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