Why this matters
- ReentrantLock — detailed pointwise breakdown in the section below.
- AtomicInteger — detailed pointwise breakdown in the section below.
- ConcurrentHashMap — detailed pointwise breakdown in the section below.
- ExecutorService — detailed pointwise breakdown in the section below.
- Concurrency appears in elevator, booking, cache, and feed problems.
Producers
BlockingQueue
Workers
Overview
Locks, atomics, concurrent collections, and executors in design problems. Study each section below in order — every list is interview-ready reference material.
ReentrantLock
Points to cover
- Definition — what ReentrantLock means in one clear sentence
- When to use — the force or smell that triggers this concept
- CampusOS example — where this appears in parking, booking, or library modules
- How to explain — pointwise bullets you can say aloud in an interview
- Common mistake — what weak candidates do instead
- Refactor move — one concrete change that improves the design
AtomicInteger
Points to cover
- Definition — what AtomicInteger means in one clear sentence
- When to use — the force or smell that triggers this concept
- CampusOS example — where this appears in parking, booking, or library modules
- How to explain — pointwise bullets you can say aloud in an interview
- Common mistake — what weak candidates do instead
- Refactor move — one concrete change that improves the design
ConcurrentHashMap
Points to cover
- Definition — what ConcurrentHashMap means in one clear sentence
- When to use — the force or smell that triggers this concept
- CampusOS example — where this appears in parking, booking, or library modules
- How to explain — pointwise bullets you can say aloud in an interview
- Common mistake — what weak candidates do instead
- Refactor move — one concrete change that improves the design
ExecutorService
Points to cover
- Definition — what ExecutorService means in one clear sentence
- When to use — the force or smell that triggers this concept
- CampusOS example — where this appears in parking, booking, or library modules
- How to explain — pointwise bullets you can say aloud in an interview
- Common mistake — what weak candidates do instead
- Refactor move — one concrete change that improves the design
// CampusOS — apply "ReentrantLock" on paper first, then in code
public final class ConcurrencyToolkitExample {
// 1. Name entities from the problem statement
// 2. Draw relationships before writing methods
// 3. Introduce patterns only when a force appears
}
Quick recall
Everything you need if you only revisit this box.
- ReentrantLock — review this slice before mock interviews.
- AtomicInteger — review this slice before mock interviews.
- ConcurrentHashMap — review this slice before mock interviews.
- ExecutorService — review this slice before mock interviews.
Test yourself
Answer these before moving on — recall is what makes it stick.