⏱️ Section 19 · 28 questions
CompletableFuture and Asynchrony
28 interview questions and answers in the CompletableFuture and Asynchrony section.
Questions in this section
- What is CompletableFuture and How Does It Differ from Future
- What Are the Main Advantages of CompletableFuture Over Future
- How to Create a CompletableFuture That is Already Completed with Result
- What is the Difference Between thenApply() and thenCompose()
- What Do thenAccept() and thenRun() Methods Do
- How to Handle Exceptions in CompletableFuture Chain
- What is the Difference Between handle(), exceptionally() and whenComplete()
- How to Combine Results of Multiple CompletableFutures
- What Does allOf() Method Do and When to Use It
- What does anyOf() method do and when is it useful
- What is the difference between thenApply() and thenApplyAsync()
- What thread pool is used by default for async methods
- How to specify your own Executor for CompletableFuture
- What is blocking code and how to distinguish it from non-blocking
- Why is it important to avoid blocking operations in CompletableFuture
- How to properly execute multiple parallel requests to microservices
- What does supplyAsync() method do and when to use it
- How to cancel CompletableFuture execution
- What happens if an exception occurs in CompletableFuture chain
- Can you reuse a single CompletableFuture in multiple chains
- How to implement timeout for CompletableFuture
- What does orTimeout() method do in Java 9+
- What is the difference between thenCombine() and thenCompose()
- How to test code with CompletableFuture
- When is it better to use CompletableFuture vs reactive programming
- What does join() method do and how does it differ from get()
- Can you manually complete a CompletableFuture with a result
- How to implement retry logic with CompletableFuture
Study navigator
28 essential questions and deep-dive architectural analyses for Junior 🟢, Middle 🟡, and Senior 🔴 Java Asynchronous, Concurrent, and High-Throughput Engineers.
📋 Table of Contents
🗺️ Topic Dependency Map
┌──────────────────────────────────────────┐
│ ASYNC FOUNDATIONS (01-03, 17, 26-27)│
│ 01-02. CompletableFuture vs Future │
│ 03, 27. Manual & Immediate Completion │
│ 17. supplyAsync & runAsync │
│ 26. join() vs get() & Exceptions │
└──────────────────┬───────────────────────┘
│
┌──────────────────────────┼──────────────────────────┐
▼ ▼ ▼
┌───────────────┐ ┌───────────────┐ ┌────────────────────┐
│ CHAINING & │ │ COMBINING & │ │ EXECUTORS & THREAD │
│ MONADS (04-05)│ │ FAN-OUT (08-10│ │ POOLS (11-15) │
│ 04. Apply/Comp│ │ 16, 23) │ │ 11. Async Variant │
│ 05. Accept/Run│ │ 08, 23. Combine│ │ 12. ForkJoinPool │
│ 20. DAG Reuse │ │ 09. allOf() │ │ 13. Custom Pool │
└───────┬───────┘ │ 10. anyOf() │ │ 14-15. Anti-Block │
│ │ 16. Svc Scatter│ └────────┬───────────┘
│ └───────┬───────┘ │
│ │ │
└────────────────────────┼─────────────────────────┘
▼
┌──────────────────────────────────────────┐
│ FAULT TOLERANCE, TIMEOUTS & OPS (06-07, │
│ 18-19, 21-22, 24-25, 28) │
│ 06-07, 19. Exception Handling Pipeline │
│ 18. Cancellation Mechanics │
│ 21-22. Timeout & orTimeout (Java 9+) │
│ 24. Deterministic Async Unit Testing │
│ 25. CF vs Project Reactor & RxJava │
│ 28. Asynchronous Exponential Retries │
└──────────────────────────────────────────┘
🎯 Recommended Study Tracks
🟢 Junior Track (Core Concepts & Pipeline Basics)
- Step 1: Future vs CompletableFuture — 01. What is CompletableFuture and How Does It Differ from Future, 02. What Are the Main Advantages of CompletableFuture Over Future, 17. What Does supplyAsync() Method Do and When to Use It
- Step 2: Basic Chaining & Transformation — 04. What is the Difference Between thenApply() and thenCompose(), 05. What Do thenAccept() and thenRun() Methods Do
- Step 3: Blocking & Result Extraction — 26. What Does join() Method Do and How Does It Differ from get(), 14. What is Blocking Code and How to Distinguish It from Non-Blocking
🟡 Middle Track (Thread Pools, Aggregations & Resilience)
- Step 1: Thread Pools & Execution Context — 11. What is the Difference Between thenApply() and thenApplyAsync(), 12. What Thread Pool is Used by Default for Async Methods, 13. How to Specify Your Own Executor for CompletableFuture
- Step 2: Combining Multiple Futures — 08. How to Combine Results of Multiple CompletableFutures, 09. What Does allOf() Method Do and When to Use It, 10. What Does anyOf() Method Do and When is It Useful, 23. What is the Difference Between thenCombine() and thenCompose()
- Step 3: Error Handling & Timeouts — 06. How to Handle Exceptions in CompletableFuture Chain, 07. What is the Difference Between handle(), exceptionally() and whenComplete(), 21. How to Implement Timeout for CompletableFuture, 22. What Does orTimeout() Method Do in Java 9+
🔴 Senior Track (Microservices Architecture, Non-Blocking Systems & Retries)
- Step 1: High-Throughput Aggregation & Anti-Patterns — 15. Why is It Important to Avoid Blocking Operations in CompletableFuture, 16. How to Properly Execute Multiple Parallel Requests to Microservices
- Step 2: Advanced Asynchronous Flow & Testing — 18. How to Cancel CompletableFuture Execution, 20. Can You Reuse a Single CompletableFuture in Multiple Chains, 24. How to Test Code with CompletableFuture
- Step 3: CompletableFuture vs Reactive & Retries — 25. When is It Better to Use CompletableFuture vs Reactive Programming, 28. How to Implement Retry Logic with CompletableFuture