Java interview questions for 3 to 5 years of experience

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OOPs – Explain core OOPs concepts like abstraction, encapsulation, inheritance and polymorphism. Difference between abstract classes and interfaces.
Exception Handling – Checked vs unchecked exceptions, try-catch-finally blocks, custom exceptions, throwing and propagating exceptions.
Multithreading – Thread lifecycle, implementing threads using Runnable and Thread class, synchronized keyword, inter-thread communication using wait(), notify() etc.
JDBC – Steps for connecting to a database, use of PreparedStatements vs Statements, handling ResultSet. Transaction management.
Collections – Commonly used methods in Map, List, Set. Difference between ArrayList and LinkedList. Comparator and Comparable.
Java 8 – Lambda expressions, method references, functional interfaces, streams, date/time API.
Spring – Dependency injection, IOC container, ApplicationContext. Spring MVC request flow, REST APIs using Spring.
Hibernate – Lazy loading, eager loading, dirty checking, caching. Hibernate annotations and configuring session factory.
Microservices – RESTful web services, challenges in microservices, API gateways, service discovery.
Design Patterns – Singleton, factory, observer, decorators, template, strategy. Experience in applying patterns.
Testing – JUnit, Mockito, mocking private/void methods, parameterized tests. Integration vs unit testing.
Build Tools – Maven, dependency management, build cycles.