#Exception-Handling

Last updated    - V6 (18-Nov-2025)

Key Concepts

Topic	Sub-Topic	Basic	Intermediate	Advanced	Expert
Exception Basics	Exception, Error vs Exception, Exception hierarchy, Checked vs Unchecked	✅
Try-Catch-Finally	try block, catch block, multiple catch, finally block, nested try-catch	✅	✅
Throw & Throws	throw keyword, throws keyword, difference, use cases	✅	✅
Custom Exceptions	User-defined exceptions, Extending Exception class, Extending RuntimeException class		✅	✅
Exception Propagation	Call stack propagation, rethrowing exceptions, handling vs declaring		✅	✅
Multi-Catch & Re-throw	Multi-catch (Java 7+), Rethrowing exceptions, Exception wrapping		✅	✅
Try-with-Resources	AutoCloseable, Suppressed exceptions, Resource management		✅	✅
Best Practices	Checked vs unchecked choice, meaningful messages, logging, avoiding empty catch	✅	✅	✅	✅
Exception Hierarchy	Throwable, Error, Exception, RuntimeException, Custom hierarchy	✅	✅	✅
Overriding & Exceptions	Exception rules in overriding, narrower exceptions, throws clause differences		✅	✅
Performance Impacts	Cost of exceptions, Alternatives to exceptions, Avoiding overuse			✅	✅
Streams	Stream pipelines, lambda expressions, handling checked exceptions in lambdas			✅	✅
Framework-Specific	Spring @ExceptionHandler, REST Exception Mappers, JUnit expected exceptions			✅	✅
Advanced Scenarios	Exception translation, Exception chaining, Domain-specific exceptions, Retry strategies			✅	✅
System-Level Exceptions	JVM errors, OutOfMemoryError, StackOverflowError, Fatal exceptions			✅	✅
Design Patterns & Exceptions	Try-catch-finally pattern, Command pattern with exceptions, Checked-to-unchecked conversion			✅	✅
Logging & Monitoring	Logging frameworks (SLF4J/Log4j), Correlation IDs, Centralized monitoring			✅	✅
Distributed Systems	Exception handling across services, retries, circuit breakers, fallback strategies			✅	✅
Expert Practices	Fail-fast vs fail-safe, Error boundaries, Designing exception-safe APIs			✅	✅

Interview question

Basic Level

• What is an exception?
• What is the difference between an error and an exception?
• What is the difference between checked and unchecked exceptions?
• What is a try-catch block?
• What is the purpose of the finally block?
• How do you throw an exception explicitly?
• What is the throws keyword?
• What is the difference between throw and throws?
• What is a custom exception?
• How do you create a custom exception?
• What is the call stack when an exception occurs?
• How do you print a stack trace?
• What is exception propagation?
• What happens if an exception is not caught?
• What is the default exception handler?
• What is an InterruptedException and when is it thrown?
• What is NullPointerException and common causes?
• What is ArrayIndexOutOfBoundsException?
• What is ArithmeticException?
• What is ClassCastException?
• How do you catch multiple exceptions in a single catch block?
• What is multi-catch in Java?
• What is the purpose of Exception class?
• Can you catch Throwable? Should you?
• What is the effect of returning from a finally block?

Intermediate Level

• What is exception chaining (cause)?
• How do you set the cause of an exception?
• What is suppression of exceptions?
• How does try-with-resources work?
• What are suppressed exceptions in try-with-resources?
• What is the AutoCloseable interface?
• How do you design exception messages?
• What is exception translation/wrapping and why use it?
• What are best practices for logging exceptions?
• When should you rethrow an exception?
• What is a fatal exception vs recoverable exception?
• How do you implement retry logic safely?
• What is circuit breaker pattern related to exceptions?
• How do you handle exceptions in API boundaries?
• What is error handling strategy in layered architecture?
• How to avoid swallowing exceptions?
• What is defensive programming with exceptions?
• How do you test exception-throwing code?
• How do you assert exceptions in unit tests?
• What is the role of exception handling in transactions?
• How do exceptions affect transactions (rollback)?
• How to create meaningful exception hierarchies?
• What are checked exceptions vs unchecked in API design?
• When to use checked exceptions?
• When to use unchecked exceptions?

Advanced Level

• How do exceptions affect performance?
• What is the cost of throwing exceptions vs checking conditions?
• How does JVM handle stack traces for exceptions?
• What is enabling/disabling stack trace generation (Throwable.fillInStackTrace)?
• What is exception-safe code and strong exception safety guarantees?
• How to implement circuit breakers with exception patterns?
• How to design retry/backoff strategies for transient exceptions?
• How to map exceptions to appropriate HTTP status codes?
• What is the role of correlation IDs when handling exceptions in distributed systems?
• How do you implement global exception handlers in web frameworks (e.g., Spring)?
• How to propagate exceptions across threads and executors?
• How to capture exceptions from CompletableFuture or async APIs?
• How to implement exception translation across layers?
• How do you differentiate transient vs permanent exceptions programmatically?
• What is the role of idempotency when retrying after exceptions?
• How to perform fault injection and chaos testing for exception scenarios?
• How to detect and handle resource exhaustion exceptions?
• How to design resilient fallbacks for failed operations?
• What are common anti-patterns in exception handling?
• How to handle exceptions in streaming or reactive pipelines?
• How to debug memory leaks caused by exception-related resource leaks?

Expert Level

• How to design a global error handling strategy for microservices?
• How to ensure observability of exception events (traces, metrics, logs)?
• How to design exception taxonomies for large codebases?
• How to perform exception-driven feature flags and graceful degradation?
• How to use typed error responses in public APIs while hiding internal details?
• How to ensure security when exposing exception information?
• How to correlate user requests with exception traces across services?
• How to build a centralized exception collection and analysis pipeline?
• How to use machine learning to detect anomalous exception patterns?
• How to design for eventual consistency and exception recovery in distributed transactions?
• How to handle partial failures in distributed systems?
• What are best practices for exception handling in high-throughput low-latency systems?
• How to minimize exception overhead in hot code paths?
• How to use custom exception serializers for cross-language systems?
• How to implement graceful shutdown with exception cleanup in concurrent services?
• How to design contract-based error handling (e.g., gRPC status codes)?
• How to handle exceptions originating from third-party libraries effectively?
• How to manage breaking changes in exception types across API versions?
• How to perform post-mortem and RCA for recurring exceptions?
• How to build automated remediation for known exception patterns?

Bonus: Quick Practicals / Coding Prompts

• Write code that demonstrates try-with-resources with multiple resources and suppressed exceptions.
• Implement a custom checked exception and use it in a sample API.
• Create a utility that converts stack traces to a structured JSON format for logging.
• Implement retry logic with exponential backoff for a transient IO exception.
• Demonstrate exception propagation across threads using ExecutorService and Future.
• Show how to safely close resources even when exceptions are thrown.
• Implement a global exception handler in a Spring Boot REST API.
• Write unit tests that assert specific causes of exceptions.
• Demonstrate wrapping and unwrapping exceptions while preserving the original cause.
• Implement a simple circuit breaker that trips on repeated exceptions.

Related Topics

Exception Basics

Exception Hierarchy

Throw & Throws

Custom Exceptions

Built-in Exceptions