Object-Oriented Programming (OOP) Encapsulation: Bundling data and methods that operate on the data within one unit (class), restricting access to some of the object's components. Inheritance: Mechanism to create new classes using the properties and methods of an existing class. Polymorphism: Ability to process objects differently based on their data type or class. Abstraction: Hiding complex implementation details and showing only the essential features of an object. 2. Java Core Concepts Concurrency: Handling multiple tasks simultaneously (using threads, executors, etc.). Memory Management: Garbage collection, stack vs heap memory, memory leaks. Streams and Lambdas: Modern ways to handle collections and data transformations in a functional style (Java 8+). Exceptions: Error handling with try-catch blocks, custom exceptions, and best practices. JVM Internals: Understanding the JVM (Java Virtual Machine), its garbage collection strategies, and performance tuning. 3. Hibernate & ORM (Object-Relational Mapping) Entity Mapping: Using annotations or XML configuration to map Java objects to database tables. Lazy vs Eager Loading: Performance trade-offs when loading associated entities. Caching: First-level and second-level caches to optimize data retrieval and persistence. Criteria API vs HQL: Programmatic querying with Criteria API or Hibernate Query Language (HQL).