#Exception-Handling

Last updated    - V7 (19-Dec-2025)

Key Concepts

S.No	Topic	Sub-Topics
1	Introduction	Definition, Errors vs Exceptions, Exception flow, Why needed, Real-world examples
2	Exception Types	Checked, Unchecked, Errors, Runtime, Throwable hierarchy
3	try-catch Basics	Syntax, Single catch, Exception capture, Debugging, Execution flow
4	Multiple catch	Multiple catch block, Order, Specific vs Generic, Multi-catch Java 7, Best practices
5	finally Block	Execution guarantee, Use cases, Resource cleanup, Try-finally, Finally behavior
6	throw Keyword	Manual throwing, Use cases, Custom messages, Runtime behavior, Stack trace
7	throws Keyword	Method signature, Propagation, Checked declaration, Compile errors, Best use
8	Exception Propagation	Call stack, Propagation rules, try vs throws, Runtime behavior, Examples
9	Custom Exceptions	Create class, Extend Exception, Extend RuntimeException, Fields, Constructors
10	Exception Class Hierarchy	Throwable, Error, Exception, RuntimeException, Libraries
11	Common Exception Types	NullPointer, ArrayIndex, Arithmetic, IO, ClassCast
12	Stack Trace	Print stack trace, Logging stack trace, Trace format, Frames, Debugging
13	Best Practices	Avoid swallowing, Custom messages, Single responsibility, Fail fast, Graceful exit
14	Checked vs Unchecked	Difference, When to use, Design patterns, Pros/Cons, Standards
15	Resource Management	I/O exceptions, Close resources, try-catch-finally, Auto close, Patterns
16	Try-with-resources	Java 7 feature, AutoCloseable, Multiple resources, Suppressed exceptions, Syntax
17	Suppressed Exceptions	Meaning, Access suppressed, PrintStackTrace, Use cases, Resource conflict
18	Logging Basics	Why log, Log levels, Log format, Logger libraries, Writing log
19	Advanced Logging	SLF4J, Logback, Log4j, Pattern layout, Exception logging
20	Exception Translation	Mapping exceptions, Wrapping error, Abstraction, custom messages, Conversion
21	Global Exception Handling	Application-level handling, Default handlers, Hooks, Web apps, Spring global handler
22	Spring Exception Handling	@ExceptionHandler, @ControllerAdvice, Custom response, JSON errors, Logging
23	Unit Testing Exceptions	JUnit test, assertThrows, Expected exceptions, Boundary cases, Testing messages
24	Debugging Techniques	Breakpoints, Watches, IDE tools, Visual debug, Exception inspect
25	Design Patterns	Command pattern exceptions, Builder validation, Strategy fallback, Template hook, Fail-safe
26	Performance Considerations	Cost of exceptions, Avoid overuse, Try/catch slow paths, Control flow bad practice, Benchmarks
27	Enterprise Handling	API error model, Status codes, Error JSON, Unified error format, Standards
28	Exception Metrics	Monitoring, Counters, Failure rate, Alerting, Dashboard
29	Security & Exceptions	Leaking info, Sanitizing output, Stack trace risk, Error pages, Secure messages
30	Interview Prep	Top 20 questions, Live coding, Common traps, Custom design, Real project demo

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

#Collections

Last updated    - V7 (12-Jan-2026)

Key Concepts

S.No	Topic	Sub-Topics
1	Collections	Collection, Collection vs Collections, Hierarchy, Root Interfaces, Use Cases
2	Core Interfaces	Collection, List, Set, Map, Queue, Marker Interfaces
3	Iterable & Iterators	Iterable, Iterator, ListIterator, forEach, Fail-fast
4	List Interface	Indexed Access, Order, Duplicate, add/remove, ListIterator
5	ArrayList	Internal Array, resize, load factor, random access, use cases
6	LinkedList	Doubly Linked, node structure, insertion cost, Deque support, use cases
7	Vector & Stack	Legacy Classes, Synchronization, performance, Stack methods, use cases
8	Set Interface	Uniqueness, hashing logic, duplicate detection, equals, hashCode
9	HashSet	Hash table, buckets, collisions, load factor, iterator order
10	LinkedHashSet	Insertion order, doubly-linked buckets, access order, LRU
11	TreeSet	Sorted, NavigableSet, Red-Black Tree, compareTo, Comparator
12	Map Interface	Key/Value, uniqueness of key, null handling, entrySet, hashing
13	HashMap	Hashing, buckets, resizing, tree bins, load factor, collisions
14	LinkedHashMap	Order, access-order mode, LRU cache, removeEldestEntry, use cases
15	TreeMap	Red-Black Tree, sorting keys, NavigableMap, comparator, range queries
16	ConcurrentHashMap	Segments, Lock-free, CAS, performance, concurrency model
17	WeakHashMap	GC aware keys, WeakReference, caching, memory leaks
18	IdentityHashMap	Reference equality, == vs equals, special use cases, pitfalls
19	EnumMap & EnumSet	Bitwise storage, speed, memory, enum key benefits
20	Queue Interface	FIFO behavior, offer/poll, peek, priority queue, Deque
21	Deque Interface	Double-ended queue, addFirst/addLast, stack vs queue
22	PriorityQueue	Heap, priority logic, compareTo, ordering, use cases
23	BlockingQueue	Producer-consumer, put/take methods, thread safety, use cases
24	CopyOnWrite Collections	CopyOnWriteArrayList, snapshot, safety, performance trade-offs
25	Collections Utility Class	sort, reverse, shuffle, binarySearch, unmodifiable, synchronized
26	Stream Collectors	toList, toSet, toMap, groupingBy, partitioningBy, mapping
27	Custom Comparator	Comparator interface, compare method, chaining, reversed, nullsFirst
28	Big-O Performance	Complexity, add/remove, get, contains, load factor, resizing
29	Choosing Right Collection	Decision matrix, use cases, performance tuning, trade-offs
30	Best Practices & Patterns	Immutability, safe iteration, fail-fast, defensive copy, caching

Interview question

Basic

1. What is the Java Collections Framework?
2. Difference between Collection and Collections in Java?
3. What are the main interfaces in the Java Collections Framework?
4. Difference between List, Set, and Map?
5. What is the difference between Array and ArrayList?
6. What is the difference between ArrayList and LinkedList?
7. Difference between HashSet and TreeSet?
8. What is the difference between HashMap and Hashtable?
9. What is the difference between HashMap and LinkedHashMap?
10. What is the difference between HashMap and TreeMap?
11. What is the default load factor of HashMap?
12. How does HashMap handle collisions?
13. What is the initial capacity of HashMap?
14. What is the difference between fail-fast and fail-safe iterators?
15. How do you iterate over a List in Java?
16. How do you sort a List in Java?
17. How do you reverse a List in Java?
18. What is the use of Collections utility class?
19. How do you make a List thread-safe?
20. What is the difference between synchronized collections and concurrent collections?
21. What is the difference between ArrayDeque and LinkedList as a Queue?
22. What is the difference between Stack and Deque?
23. What is the difference between PriorityQueue and TreeSet?
24. How does PriorityQueue maintain ordering?
25. What is the difference between Comparable and Comparator?

---

Intermediate

1. Explain how HashMap works internally.
2. What is the role of hashCode() and equals() in collections?
3. Why are hashCode() and equals() important in HashMap/HashSet?
4. What happens if you override equals() but not hashCode()?
5. What happens if you override hashCode() but not equals()?
6. What is the difference between shallow copy and deep copy in collections?
7. How do you create an immutable collection in Java?
8. What is the difference between unmodifiable and immutable collections?
9. What are WeakHashMap and its use cases?
10. How does IdentityHashMap differ from HashMap?
11. What is EnumSet and EnumMap?
12. What is the difference between LinkedHashSet and TreeSet?
13. How does ConcurrentHashMap achieve thread safety?
14. What is the difference between CopyOnWriteArrayList and ArrayList?
15. What is the difference between ConcurrentSkipListMap and TreeMap?
16. What is the difference between BlockingQueue and ConcurrentLinkedQueue?
17. Explain how LinkedHashMap maintains insertion order.
18. What is LRU cache and how can you implement it using LinkedHashMap?
19. What are NavigableMap and NavigableSet?
20. Explain differences between TreeSet and TreeMap.
21. How do you synchronize a HashMap?
22. What is the difference between Collections.synchronizedList and CopyOnWriteArrayList?
23. What is Spliterator in Java collections?
24. How do you iterate a map using Java 8 forEach?
25. How do you convert between arrays and collections?

---

Advanced

1. Explain HashMap resizing and rehashing process.
2. What is the significance of 0.75 load factor in HashMap?
3. What happens when two keys have the same hashCode in HashMap?
4. What is the role of linked lists and balanced trees in HashMap buckets (Java 8+)?
5. Explain the performance differences between ArrayList, LinkedList, and Vector.
6. How does TreeMap ensure sorting of keys?
7. Difference between natural ordering and custom ordering in TreeMap/TreeSet?
8. How does ConcurrentHashMap split data into segments? (Java 7 vs Java 8)
9. What is the difference between parallelStream() and stream() on collections?
10. What is a fail-fast iterator? Which collections are fail-fast?
11. What is a fail-safe iterator? Which collections are fail-safe?
12. How does CopyOnWriteArrayList work internally?
13. What are weak references and how does WeakHashMap use them?
14. How does IdentityHashMap use reference equality?
15. Explain the difference between Hashtable and ConcurrentHashMap.
16. How does EnumMap achieve better performance than HashMap?
17. What are concurrent collections introduced in Java 5?
18. What is the difference between ArrayBlockingQueue and LinkedBlockingQueue?
19. How does PriorityBlockingQueue work?
20. What is DelayQueue and its use cases?
21. How does LinkedTransferQueue work?
22. What is the difference between ConcurrentLinkedDeque and ArrayDeque?
23. How do you implement producer-consumer using BlockingQueue?
24. How do you avoid ConcurrentModificationException in collections?
25. Explain the difference between Collections.emptyList() and new ArrayList<>().

---

Expert

1. Explain the red-black tree implementation in TreeMap.
2. How does HashMap deal with hash collisions after Java 8?
3. What is tail binning in ConcurrentHashMap?
4. Explain bin migration in ConcurrentHashMap.
5. What is structural modification in collections?
6. How does Java?s ForkJoinPool interact with parallel streams on collections?
7. How do you implement a custom collection in Java?
8. What interfaces must a custom collection implement?
9. How do you implement a custom comparator for complex sorting?
10. How does Spliterator support parallelism in Java collections?
11. What is the role of characteristics in Spliterator (e.g., ORDERED, DISTINCT, SIZED)?
12. How do you use Collectors.toMap() without causing IllegalStateException on duplicate keys?
13. How do you optimize collection performance for read-heavy workloads?
14. How do you optimize collection performance for write-heavy workloads?
15. How does ConcurrentSkipListMap ensure thread safety and ordering?
16. Explain the difference between segment-locking (Java 7) and bucket-level locking (Java 8) in ConcurrentHashMap.
17. How do you implement a thread-safe LRU cache?
18. Explain memory overhead of different collections.
19. How do you implement multi-level sorting using Comparator chaining?
20. How do you detect and handle memory leaks in collections?
21. How do you implement an observer pattern with collections?
22. How does the Stream API integrate with collections?
23. How do you design collections for large-scale distributed systems?
24. How do you tune GC behavior for large collections in JVM?
25. Future of Java collections: how Project Valhalla and new JVM features might affect them?

Related Topics

Collections Basic

Array

ArrayList

LinkedList

HashSet

LinkedHashSet

TreeSet

HashMap

LinkedHashMap

TreeMap

ConcurrentHashMap

WeakHashMap

IdentityHashMap

#CoreJava_08

Last updated    - V7 (19-Dec-2025)

Key Concepts

S.No	Topic	Sub-Topics
1	Java 8 Overview	Java 8 introduction, Why Java 8, Major enhancements, Backward compatibility, Java 8 use cases
2	Functional Programming	Functional programming basics, Pure functions, Immutability, Stateless behavior, Lambda-driven design
3	Lambda Expressions - Basics	Lambda syntax, Lambda parameters, Lambda body, Lambda vs anonymous class, Lambda advantages
4	Lambda Expressions - Advanced	Lambda with collections, Lambda with threads, Lambda with methods, Effectively final variables, Lambda limitations
5	Functional Interfaces	@FunctionalInterface , Single abstract method, Lambda compatibility, Custom functional interfaces
6	Built-in Functional Interfaces	Predicate, Function, Consumer, Supplier, Bi-functional interfaces
7	Predicate Interface	test() method, Predicate chaining, and(), or(), negate(), Real-time examples
8	Function Interface	apply() method, Function chaining, compose(), andThen(), Real-time use cases
9	Consumer Interface	accept() method, Consumer chaining, forEach usage, Logging examples, Printing data
10	Supplier Interface	get() method, Lazy value generation, Supplier vs Function, Factory usage, Random value generation
11	Method References	Static method reference, Instance method reference, Constructor reference, Syntax (::), Lambda replacement
12	Stream API - Introduction	What is stream, Stream vs collection, Stream pipeline, Intermediate operations, Terminal operations
13	Stream Creation	Stream from collection, Stream.of(), Arrays.stream(), Infinite streams, Empty streams
14	Stream Intermediate Operations	filter(), map(), flatMap(), distinct(), sorted()
15	Stream Terminal Operations	forEach(), collect(), reduce(), count(), findFirst()
16	Stream Collectors	Collectors.toList(), toSet(), toMap(), groupingBy(), partitioningBy()
17	Stream Reduction Operations	reduce() method, Identity value, Accumulator, Combiner, Aggregation examples
18	Parallel Streams	parallelStream(), ForkJoinPool, Performance benefits, Thread safety issues, When to use parallel streams
19	Optional Class	Optional creation, isPresent(), ifPresent(), orElse(), orElseThrow()
20	Default Methods in Interface	Default method syntax, Multiple inheritance resolution, Diamond problem, Overriding defaults, Use cases
21	Static Methods in Interface	Static method rules, Invocation syntax, Difference from default methods, Utility methods, Best practices
22	ForEach Method	Iterable forEach(), Lambda usage, Method reference usage, Internal iteration, Comparison with loops
23	Nashorn JavaScript Engine	Nashorn overview, JavaScript execution, ScriptEngine API, Java-JS interaction, Use cases
24	New Date & Time API - Basics	Problems with old Date API, LocalDate, LocalTime, LocalDateTime, Immutability
25	New Date & Time API - Advanced	ZonedDateTime, Period, Duration, DateTimeFormatter, Time zones
26	CompletableFuture	Future limitations, CompletableFuture basics, Async execution, thenApply(), thenAccept()
27	Collectors Grouping & Partitioning	groupingBy(), partitioningBy(), downstream collectors, Multi-level grouping, Real examples
28	Stream Performance	Lazy evaluation, Short-circuiting, Stream reuse rules, Avoiding side effects, Performance tuning
29	Java 8 Coding Patterns	Filter-map-reduce pattern, Functional pipelines, Optional usage patterns, Lambda best practices, Stream refactoring
30	Java 8 Revision & Interview Prep	Java 8 feature recap, Common interview questions, Coding scenarios, Performance discussions, Best practices

Interview question

Basic Level

1. What are the major features introduced in Java 8?
2. Why was Java 8 introduced?
3. What is functional programming in Java 8?
4. What is a lambda expression?
5. What problems do lambda expressions solve?
6. What is the syntax of a lambda expression?
7. Difference between lambda expression and anonymous class?
8. What is a functional interface?
9. What is @FunctionalInterface annotation?
10. Can a functional interface have default methods?
11. Can a functional interface have static methods?
12. What are built-in functional interfaces?
13. What is Predicate interface?
14. What is Function interface?
15. What is Consumer interface?
16. What is Supplier interface?
17. What is method reference?
18. Types of method references?
19. What is Stream API?
20. Why streams are introduced?
21. Difference between stream and collection?
22. What is stream pipeline?
23. What are intermediate operations?
24. What are terminal operations?
25. What is forEach() method?

Intermediate Level

26. How to create a stream?
27. What is filter() in streams?
28. What is map() in streams?
29. Difference between map() and flatMap()?
30. What is distinct()?
31. What is sorted()?
32. What is limit() and skip()?
33. What is collect()?
34. What is Collectors class?
35. What is Collectors.toList()?
36. What is Collectors.toSet()?
37. What is Collectors.toMap()?
38. What is groupingBy()?
39. What is partitioningBy()?
40. Difference between groupingBy and partitioningBy?
41. What is reduce() operation?
42. What is Optional class?
43. Why Optional was introduced?
44. How to create Optional?
45. Difference between orElse() and orElseGet()?
46. What is ifPresent()?
47. What are default methods?
48. Why default methods are introduced?
49. What is static method in interface?
50. Can we override default methods?

Advanced Level

51. How lambda expressions work internally?
52. What is effectively final variable?
53. Why local variables must be effectively final in lambda?
54. How streams process data internally?
55. What is lazy evaluation in streams?
56. What is short-circuiting in streams?
57. What is findFirst()?
58. What is findAny()?
59. Difference between findFirst and findAny?
60. What is anyMatch(), allMatch(), noneMatch()?
61. What are parallel streams?
62. Difference between stream() and parallelStream()?
63. When should we use parallel streams?
64. Problems with parallel streams?
65. What is ForkJoinPool?
66. How parallel stream uses ForkJoinPool?
67. What is Java 8 Date and Time API?
68. Problems with old Date API?
69. What is LocalDate?
70. What is LocalTime?
71. What is LocalDateTime?
72. What is ZonedDateTime?
73. What is Period?
74. What is Duration?
75. What is DateTimeFormatter?

Expert Level

76. How groupingBy works internally?
77. What are downstream collectors?
78. How to perform multi-level grouping?
79. How reduce() works internally?
80. Difference between reduce() and collect()?
81. How Optional avoids NullPointerException?
82. Anti-patterns of Optional?
83. Exception handling in lambda expressions?
84. Exception handling in streams?
85. How to debug stream pipelines?
86. Performance comparison: stream vs loop?
87. When streams should be avoided?
88. CompletableFuture introduction?
89. Difference between Future and CompletableFuture?
90. What is thenApply()?
91. What is thenAccept()?
92. What is thenCombine()?
93. What is async execution in Java 8?
94. What is Nashorn JavaScript engine?
95. Use cases of Nashorn?
96. Best practices for lambda expressions?
97. Best practices for Stream API?
98. Java 8 real-time project use cases?
99. Common Java 8 interview traps?
100. Java 8 coding round expectations?

Related Topics

Functional Interfaces

Lambda Expressions

Stream API

Built-in Functional Interfaces

Optional Class

Default Method