Persistent Systems Interview Questions

#1What is the difference between == and .equals() in Java?

#2What is the difference between abstract class and interface?

#3Explain the SOLID principles.

#4How does HashMap work internally?

#5What is the difference between HashMap and ConcurrentHashMap?

#6Explain Java Memory Model: Heap, Stack, and Metaspace.

#7What is the volatile keyword in Java?

#8What are functional interfaces and lambda expressions in Java 8?

#9What is Optional and when should you use it?

#10Explain the Stream API and intermediate vs terminal operations.

#11What is the difference between checked and unchecked exceptions?

#12What is the difference between String, StringBuilder, and StringBuffer?

#13What is method overloading vs method overriding?

#14What is the difference between final, finally, and finalize?

#15What are Java records (Java 16+)?

#16What is the Executor framework and when would you use it over raw Threads?

#17What is encapsulation and how is it achieved in Java?

#18What is polymorphism? Explain runtime vs compile-time polymorphism.

#19What is the difference between composition and inheritance?

#20What is a marker interface? Give examples.

#21What are the design patterns most commonly asked in Java interviews?

#22What is the difference between ArrayList and LinkedList?

#23What is the difference between HashSet, LinkedHashSet, and TreeSet?

#24What is the difference between HashMap and TreeMap?

#25What is the contract between equals() and hashCode()?

#26What is the difference between fail-fast and fail-safe iterators?

#27What is CopyOnWriteArrayList and when should you use it?

#28How does PriorityQueue work and when would you use it?

#29What is the difference between sleep(), wait(), and yield()?

#30What are atomic classes (AtomicInteger, AtomicReference)? How do they work?

#31What is a CountDownLatch vs CyclicBarrier?

#32What is the difference between JDK, JRE, and JVM?

#33What is the String pool and how does string interning work?

#34What are sealed classes (Java 17)?

#35What is pattern matching for instanceof (Java 16)?

#36What are text blocks (Java 15)?

#37What is the difference between map() and flatMap() in streams?

#38What are method references in Java 8?

#39What is the difference between Comparable and Comparator?

#40What is Stream.collect() and what are common Collectors?

#41What is try-with-resources and how does it work?

#42What is the difference between throw and throws?

#43What is exception chaining and why is it important?

#44What is the difference between Java IO and NIO?

#45What is reflection in Java and when is it used?

#46What is the difference between deep copy and shallow copy?

#47What is autoboxing and unboxing? What are the performance implications?

#48What are enums in Java and what advanced features do they support?

#49What is the difference between static and instance initializer blocks?

#50What is the difference between String.format() and String.formatted()?

#51What is the var keyword (Java 10) and when should you use it?

#52What is the difference between an inner class, static nested class, and anonymous class?

#53What are the new switch expressions (Java 14)?

#54What is the difference between Runnable, Callable, and Future?

#55What is the difference between String.equals() and String.equalsIgnoreCase()?

#56What is the difference between Iterator and ListIterator?

#57What is the difference between abstract class and concrete class?

#58How do you handle NullPointerException in Java?

#59What is the Collections utility class? What are its most important methods?

#60What is the difference between Deque and Queue?

#61What is the difference between checked and unchecked exceptions — best practices for APIs?

#62What is the ternary operator and the null-coalescing equivalent in Java?

#63What is the difference between == null check and Objects.isNull()?

#64What is the difference between interface default methods and abstract class methods?

#65What is the difference between Iterable and Iterator?

#66What are the best practices for writing clean Java code?

#67What is the difference between a process and a thread in Java?

#68What is a race condition and how do you prevent it?

#69What is the difference between HashMap.computeIfAbsent() and getOrDefault()?

#70What is the purpose of the transient keyword?

#71What is the difference between i++ and ++i in Java?

#72What are the Java 8 Date/Time APIs and why were they introduced?

#73What is the difference between HashMap.put() and HashMap.putIfAbsent()?

#74What is the difference between String.valueOf() and toString()?

#75What is an immutable class and how do you create one?

#76What is the covariant return type in Java?

#77What is the difference between static and instance methods?

#78What is the difference between Predicate.and(), Predicate.or(), and Predicate.negate()?

#79What is the Observer pattern and how is it implemented in Java?

#80What is the Strategy pattern in Java?

#81What are the key differences between Java 8, 11, 17, and 21?

#82What is auto-configuration in Spring Boot?

#83What is @SpringBootApplication and what does it do?

#84What is IoC (Inversion of Control) and Dependency Injection?

#85What is the difference between @Component, @Service, and @Repository?

#86What is the difference between @Controller and @RestController?

#87How does Spring Boot handle exceptions globally?

#88What is Spring Boot Actuator?

#89What is the difference between @Bean and @Component?

#90Explain Spring Bean scopes.

#91How do you configure Spring profiles?

#92What is @Async in Spring Boot and how does it work?

#93What is Spring Data JPA and how does it simplify data access?

#94How does Spring Boot externalized configuration work?

#95What is Spring Cache Abstraction and how do you use it?

#96What are Spring Boot starters and why are they useful?

#97How do you write integration tests in Spring Boot?

#98What is the Spring ApplicationContext and how does it differ from BeanFactory?

#99What is the @PostConstruct and @PreDestroy lifecycle?

#100What is @Qualifier and when do you need it?

#101What is @ConfigurationProperties and how does it differ from @Value?

#102What is Spring Boot's embedded server and how do you switch from Tomcat to Undertow?

#103What is Spring's @EventListener and ApplicationEvent?

#104What is Spring Boot DevTools?

#105What is the difference between @RequestParam, @PathVariable, and @RequestBody?

#106How do you implement request validation in Spring Boot?

#107What is ResponseEntity and when should you use it?

#108What is content negotiation in Spring MVC?

#109How do you implement pagination and sorting in Spring Boot?

#110How do you version a REST API in Spring Boot?

#111What is the difference between findById() and getById() in Spring Data JPA?

#112What is the difference between @OneToMany with fetch LAZY vs EAGER?

#113What is CSRF and how does Spring Security handle it?

#114What is the difference between @Secured, @PreAuthorize, and @RolesAllowed?

#115What is CORS and how do you configure it in Spring Boot?

#116What is MockMvc and how do you use it?

#117What is @MockBean vs @Mock in Spring Boot tests?

#118What is @DataJpaTest and how does it differ from @SpringBootTest?

#119What is Testcontainers and how does it improve Spring Boot tests?

#120What is Micrometer and how does it integrate with Spring Boot Actuator?

#121How do you implement custom health indicators in Spring Boot?

#122What is graceful shutdown in Spring Boot and how do you configure it?

#123What is @ControllerAdvice and how does it work?

#124What is Spring's @Scheduled and how do you configure it?

#125What is CommandLineRunner and ApplicationRunner?

#126What is Spring Boot's banner and how can you customize it?

#127What is Spring Retry and how do you use it?

#128What is @Transactional readOnly = true and what does it optimize?

#129How do you handle file uploads in Spring Boot?

#130What is the difference between @RequestMapping and specific mapping annotations?

#131What is the difference between @Transactional on a class vs a method?

#132What is Spring Boot's connection pool? How do you tune HikariCP?

#133What is Spring Boot's auto-configuration for messaging (RabbitMQ / Kafka)?

#134How does Spring Boot handle environment-specific properties?

#135What is the purpose of @EnableJpaAuditing?

#136What is the difference between eager and lazy initialization in Spring Boot?

#137What is Spring Boot's support for caching with Redis?

#138What is Spring Boot's support for MongoDB?

#139What is the difference between @Valid and @Validated in Spring?

#140What is Spring Data REST and how does it differ from Spring MVC?

#141What is the difference between @Inject and @Autowired?

#142What is Flyway and how does it integrate with Spring Boot?

#143What are Spring Boot's management endpoints and how do you secure them?

#144What is Spring Boot's Docker image building support?

#145What is the difference between @SpringBootTest(webEnvironment) options?

#146What is Spring Boot's support for SSE (Server-Sent Events)?

#147What are microservices and what problems do they solve?

#148What is an API Gateway and what does it do?

#149How do microservices communicate?

#150What is service discovery in microservices?

#151What is the Circuit Breaker pattern and how does it prevent cascading failures?

#152What is distributed tracing and why is it important?

#153What is the Strangler Fig pattern for microservices migration?

#154How do you manage configuration in microservices?

#155What are the 12-Factor App principles?

#156What is event-driven architecture and when should you use it?

#157How do you test microservices effectively?

#158What is the circuit breaker pattern?

#159What is service discovery and how does it work?

#160What is the Bulkhead pattern?

#161What is the Retry pattern and how do you implement it safely?

#162What is the Backend for Frontend (BFF) pattern?

#163How do you implement distributed tracing?

#164What is the Strangler Fig pattern for migrating a monolith?

#165How do you version microservice APIs?

#166What is the Sidecar pattern?

#167What is a dead letter queue and why is it important?

#168How do you implement health checks in microservices?

#169What are the 12-Factor App principles?

#170What is the Ambassador pattern in microservices?

#171What is the Throttling pattern and how does it differ from rate limiting?

#172How do you test microservices?

#173What is service isolation and why is it important?

#174What is an Event-Driven Architecture?

#175What is the Role of API composition in microservices?

#176What is graceful degradation in microservices?

#177How do you implement logging in a microservices environment?

#178How do you handle timeouts in microservices?

#179What is the Scatter-Gather pattern?

#180What is the difference between a microservice and a nanoservice?

#181How do you implement canary deployments in microservices?

#182What is a Service Registry?

#183What is blue-green deployment and how does it work?

#184What is the Aggregator pattern?

#185How do microservices handle configuration management?

#186What is the Proxy pattern in microservices?

#187What is Kafka and why is it popular in microservices?

#188What is the difference between a monolith, microservices, and modular monolith?

#189What is a composite microservice?

#190How do you deal with "chatty" microservices?

#191What is the Anti-Corruption Layer pattern?

#192What are the common pitfalls of microservices adoption?

#193What is the difference between orchestration and choreography?

#194What is load shedding?

#195What is the difference between gRPC and REST for inter-service communication?

#196What is the Gateway Aggregation pattern vs Gateway Routing?

#197What is the Open Host Service pattern?

#198How do you implement service-level SLOs in microservices?

#199What is the Claim Check pattern?

#200What is the difference between horizontal and vertical scaling for microservices?

#201What is the role of a message schema registry?

#202How do you handle service discovery with Kubernetes?

#203What is the Publisher-Subscriber (Pub-Sub) pattern?

#204How do you use feature toggles in microservices?

#205What is polyglot persistence in microservices?

#206What is the Retry pattern and when should you NOT retry?

#207When should you NOT use microservices?

#208What are the different types of SQL JOINs?

#209How does indexing work in MySQL (InnoDB)?

#210What is a covering index?

#211How do you use EXPLAIN to analyze a query?

#212What are CTEs (Common Table Expressions) and when should you use them?

#213What is the N+1 query problem and how do you fix it?

#214What is a deadlock in MySQL and how does it occur?

#215What is the difference between DELETE, TRUNCATE, and DROP?

#216What is database normalization?

#217What is GROUP BY vs HAVING in SQL?

#218What is a stored procedure and when should you use it?

#219What is the difference between UNION and UNION ALL?

#220What is the difference between a clustered and a non-clustered index?

#221How does MySQL handle AUTO_INCREMENT?

#222What are covering indexes and how do they improve performance?

#223What is the EXPLAIN output and how do you read it?

#224What are database triggers and when should you avoid them?

#225What is a foreign key constraint and what are its performance implications?

#226What is the difference between CHAR and VARCHAR?

#227How do you implement full-text search in MySQL?

#228What is the difference between MyISAM and InnoDB?

#229What are MySQL stored procedures and when should you use them?

#230How do you perform a slow query analysis in MySQL?

#231What is the difference between HAVING and WHERE?

#232What is MySQL's query cache and why was it removed?

#233How do you back up a MySQL database without downtime?

#234What is the difference between optimistic and pessimistic locking in MySQL?

#235What is the difference between IN, EXISTS, and JOIN for subqueries?

#236How do you implement pagination in MySQL efficiently?

#237What are the different types of JOINs in MySQL?

#238What is the difference between a view and a materialized view?

#239What are common MySQL performance anti-patterns?

#240What is a generated column in MySQL?

#241What are the best practices for MySQL schema design?

#242How do you use MySQL's JSON column type?

#243What is ProxySQL and how is it used?

#244How do you detect and fix index fragmentation in MySQL?

#245What are the MySQL 8.0 improvements over MySQL 5.7?

#246How do you design a schema for audit logging?

#247What is the difference between COUNT(*), COUNT(1), and COUNT(col)?

#248How do you implement soft delete in MySQL?

#249What is the difference between CHAR, VARCHAR, TEXT, and BLOB?

#250What is the difference between schema-on-write and schema-on-read?

#251How do you handle time zones in MySQL?

#252What is the difference between a unique constraint and a unique index?

#253How do you monitor MySQL in production?

#254What are window functions and how do you use them?

#255What is the difference between a primary key and a unique key?

#256How do you use MySQL's event scheduler?

#257What is the EXPLAIN ANALYZE command?

#258How do you handle database connection failures in application code?

#259What is the MySQL query execution order?

#260How do you scale MySQL reads?

#261What is the difference between row-based and statement-based replication?

#262How do you use CTEs (Common Table Expressions) effectively?

#263What is the difference between TRUNCATE, DELETE, and DROP?

#264How do you implement optimistic locking with versioning in MySQL?

#265What are the different ways to copy a table in MySQL?

#266What is the purpose of the information_schema?

#267How do you implement full-table search across millions of rows efficiently?

#268What is the max_connections parameter and how do you tune it?

#269What is the difference between ROLLUP and CUBE in SQL?

#270How do you handle NULL values in MySQL queries?

#271What is the difference between a read and a write transaction?

#272What is the mysql.user table and how does MySQL authentication work?

#273What are MySQL's data types for storing money?

#274What is the difference between DATETIME and TIMESTAMP in MySQL?