Java 2 Interview Questions and Answers for 5 years experience
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What is the difference between `==` and `.equals()` in Java?
- Answer: `==` compares memory addresses for primitive types and object references. `.equals()` compares the content of objects. For Strings and other objects, you should almost always use `.equals()` to check for equality of value, not reference.
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Explain the concept of garbage collection in Java.
- Answer: Garbage collection is the automatic memory management process in Java. The JVM automatically reclaims memory occupied by objects that are no longer referenced by the program. This prevents memory leaks and simplifies development.
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What are different types of collections in Java? Give examples of when you'd use each.
- Answer: Java offers various collections like Lists (ArrayList, LinkedList), Sets (HashSet, TreeSet), and Maps (HashMap, TreeMap). ArrayLists are good for indexed access, LinkedLists for frequent insertions/deletions. HashSets provide fast lookups, TreeSets maintain sorted order. HashMaps offer fast key-value access, TreeMaps maintain sorted order by key.
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What is the difference between an interface and an abstract class?
- Answer: An interface can only contain method signatures and constants, while an abstract class can have both method signatures and method implementations (though some methods can remain abstract). A class can implement multiple interfaces but only extend one abstract class (or class).
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Explain the concept of polymorphism in Java.
- Answer: Polymorphism allows objects of different classes to be treated as objects of a common type. This is achieved through inheritance and interfaces. It enables writing flexible and reusable code.
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What are Java Generics? Why are they useful?
- Answer: Generics allow you to write type-safe code that works with various data types without losing type information at compile time. They prevent runtime `ClassCastException` errors and improve code readability.
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Explain Exception Handling in Java. What are checked and unchecked exceptions?
- Answer: Exception handling involves using `try`, `catch`, and `finally` blocks to manage exceptions. Checked exceptions (like `IOException`) must be handled explicitly, while unchecked exceptions (like `NullPointerException`) are runtime exceptions.
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What is the difference between `throw` and `throws` keywords?
- Answer: `throw` is used to explicitly throw an exception, while `throws` is used in a method signature to declare that the method might throw certain exceptions.
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What is a deadlock? How can you prevent it?
- Answer: A deadlock occurs when two or more threads are blocked indefinitely, waiting for each other to release resources. Prevention strategies include avoiding circular dependencies in resource locking, using timeouts for acquiring locks, and employing a consistent locking order.
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Explain the concept of multithreading in Java.
- Answer: Multithreading allows multiple threads to execute concurrently within a single program, improving performance and responsiveness, especially in I/O-bound applications.
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What is the difference between `synchronized` and `volatile` keywords?
- Answer: `synchronized` provides exclusive access to a method or block of code, preventing race conditions. `volatile` ensures that changes to a variable are immediately visible to other threads, avoiding caching issues but not providing atomic operations for complex data structures.
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What are Java Streams? What are their advantages?
- Answer: Java Streams provide a functional approach to processing collections. Advantages include improved readability, conciseness, and potential for parallel processing.
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Explain Lambda Expressions in Java.
- Answer: Lambda expressions are anonymous functions that can be used to concisely represent functional interfaces. They improve code readability and enable functional programming paradigms.
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What is JDBC? How is it used to connect to a database?
- Answer: JDBC (Java Database Connectivity) is an API for connecting Java applications to relational databases. It involves loading a JDBC driver, establishing a connection, creating statements, executing queries, and handling results.
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What are design patterns? Name a few common design patterns and when you would use them.
- Answer: Design patterns are reusable solutions to common software design problems. Examples include Singleton (one instance of a class), Factory (creating objects without specifying the exact class), and Observer (defining a one-to-many dependency between objects).
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Explain SOLID principles of object-oriented design.
- Answer: SOLID principles are guidelines for writing clean, maintainable, and extensible code: Single Responsibility Principle, Open/Closed Principle, Liskov Substitution Principle, Interface Segregation Principle, Dependency Inversion Principle.
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What is Spring Framework? What are its main advantages?
- Answer: Spring is a popular Java framework that simplifies application development. Advantages include dependency injection, aspect-oriented programming, and support for various technologies.
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What is dependency injection? Explain different types of dependency injection.
- Answer: Dependency injection is a design pattern where dependencies are provided to a class instead of being created within the class. Types include constructor injection, setter injection, and interface injection.
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What is AOP (Aspect-Oriented Programming)? Give an example of when you would use it.
- Answer: AOP separates cross-cutting concerns (like logging or security) from core business logic. It's useful for modularizing these concerns and improving code maintainability.
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What is RESTful API? How do you design a RESTful API?
- Answer: RESTful API follows REST architectural constraints, using HTTP methods (GET, POST, PUT, DELETE) to interact with resources. Design involves defining resources, choosing appropriate HTTP methods, and using standard HTTP status codes.
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Explain your experience with testing in Java (unit testing, integration testing).
- Answer: [Candidate should describe their experience with JUnit, Mockito, or other testing frameworks, detailing their approach to unit and integration tests, test-driven development (TDD), and code coverage.]
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What are some common performance tuning techniques in Java?
- Answer: Techniques include using efficient data structures, optimizing algorithms, using connection pooling, caching frequently accessed data, and using profilers to identify performance bottlenecks.
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What is your experience with different Java IDEs (e.g., Eclipse, IntelliJ IDEA)?
- Answer: [Candidate should describe their preferred IDE and highlight their familiarity with features like debugging, code completion, and refactoring tools.]
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Describe a challenging technical problem you faced and how you solved it.
- Answer: [Candidate should describe a specific problem, highlighting their approach to problem-solving, the technologies used, and the outcome.]
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Explain your experience with version control systems (e.g., Git).
- Answer: [Candidate should describe their experience with Git, including branching strategies, merging, resolving conflicts, and using Git for collaborative development.]
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What are your strengths and weaknesses as a Java developer?
- Answer: [Candidate should provide honest and specific answers, focusing on both technical and soft skills. Weaknesses should be framed constructively, showing self-awareness and a desire for improvement.]
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Why are you interested in this position?
- Answer: [Candidate should demonstrate genuine interest in the company, the role, and the team, highlighting how their skills and experience align with the company's needs.]
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Where do you see yourself in 5 years?
- Answer: [Candidate should express career aspirations that are realistic and demonstrate ambition and a commitment to professional growth.]
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