Top Java 21 Interview Questions for Freshers and Experienced Developers
Prepare for Java 21 interviews with real-world questions. Master new language features, concurrency enhancements, and modern Java practices with clear answers.
45 Questions
2 Pages
Easy · Medium · Hard
Page 2 of 2
Filter:
All
Easy
Medium
Hard
1
What happens if a virtual thread blocks?
hard
virtual-threads internals
JVM parks it without blocking OS thread.
Key concept: Continuation.
Efficient resource usage.
Did you know it?
2
Can virtual threads replace thread pools?
medium
design threads
Yes, for many use cases.
Key concept: Simpler concurrency.
But still use pools for CPU-bound tasks.
Did you know it?
3
How do you create a virtual thread?
easy
threads api
Using Thread.ofVirtual().start().
Key concept: New API.
Example: Thread.startVirtualThread(() -> {});
Did you know it?
4
What is pinning in virtual threads?
hard
threads performance
Occurs when a virtual thread blocks OS thread.
Key concept: Synchronization limitation.
Avoid synchronized blocks.
Did you know it?
5
Explain carrier threads in virtual threading.
hard
threads internals
Carrier threads execute virtual threads.
Key concept: Mapping.
Multiple virtual threads share carriers.
Did you know it?
6
What is the impact of virtual threads on scalability?
medium
performance threads
Massively increases concurrent tasks.
Key concept: Lightweight execution.
Improves server throughput.
Did you know it?
7
How does Java 21 enhance switch expressions?
medium
switch language
Adds pattern matching and guards.
Key concept: Expressiveness.
Supports complex conditions.
Did you know it?
8
Explain guard clauses in switch patterns.
hard
patterns switch
Adds conditions using 'when'.
Key concept: Conditional matching.
Example: case String s when s.length()>5.
Did you know it?
9
What are sealed classes and how are they used in Java 21?
medium
sealed design
Restrict class inheritance.
Key concept: Controlled hierarchy.
Useful with pattern matching.
Did you know it?
10
How does Java 21 improve error handling in concurrent code?
hard
concurrency debugging
Structured concurrency propagates errors.
Key concept: Centralized handling.
Reduces silent failures.
Did you know it?
11
What are the risks of using virtual threads incorrectly?
hard
threads pitfalls
Pinning and resource misuse.
Key concept: Blocking operations.
Avoid synchronized I/O.
Did you know it?
12
How does Java 21 improve memory management?
medium
gc performance
Through generational ZGC.
Key concept: Reduced pauses.
Better heap utilization.
Did you know it?
13
Explain use case of sequenced map.
medium
collections map
Maintains insertion order with extra APIs.
Key concept: Order handling.
Example: reversed views.
Did you know it?
14
What is a practical use of record patterns?
medium
patterns design
Simplifies DTO handling.
Key concept: Destructuring.
Reduces boilerplate.
Did you know it?
15
How does Java 21 support modern application design?
medium
architecture modern
With improved concurrency and APIs.
Key concept: Scalability.
Supports cloud-native apps.
Did you know it?
16
Explain debugging challenges with virtual threads.
hard
debugging threads
Harder tracing due to large thread count.
Key concept: Observability.
Use improved tooling.
Did you know it?
17
What is the role of preview features in Java 21?
easy
preview features
Allows testing new features.
Key concept: Experimental APIs.
Must enable explicitly.
Did you know it?
18
How do you enable preview features?
easy
preview setup
Using --enable-preview flag.
Key concept: Compilation/runtime flag.
Required in javac and java.
Did you know it?
19
Explain impact of Java 21 on microservices.
medium
microservices performance
Improves scalability and latency.
Key concept: Lightweight threads.
Handles more requests efficiently.
Did you know it?
20
What are best practices when adopting Java 21?
medium
best-practices migration
Use virtual threads wisely and test preview features.
Key concept: Gradual adoption.
Avoid premature optimization.
Did you know it?
21
How does Java 21 improve API consistency?
medium
api design
Through sequenced collections.
Key concept: Unified operations.
Reduces API confusion.
Did you know it?
22
What are limitations of structured concurrency?
hard
concurrency limitations
Still evolving and limited tooling.
Key concept: Preview feature.
May change in future.
Did you know it?
23
How does Java 21 enhance code readability?
medium
readability syntax
Through pattern matching and templates.
Key concept: Declarative style.
Less boilerplate.
Did you know it?
24
What is a real-world scenario for virtual threads?
medium
use-case threads
Handling HTTP requests in web servers.
Key concept: High concurrency.
Thousands of clients handled efficiently.
Did you know it?
25
Compare Java 21 with previous LTS versions.
medium
comparison lts
Java 21 adds major concurrency improvements.
Key concept: Evolution.
Focus on scalability and developer productivity.
Did you know it?
0 / 0 answered
