Java Freshers Interview Questions and Answers for 7 years experience

Note: This focuses on fundamental Java concepts with a slightly advanced twist to reflect 7 years of *claimed* experience, addressing the inherent contradiction of "7 years experience, Java Freshers". The answers assume a basic understanding of Java. A candidate claiming 7 years experience should provide much more detailed and nuanced answers.

1. 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 always use .equals() for content comparison. For primitive types, only == is applicable.

2. 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 more flexible and reusable code.

3. What is the difference between an interface and an abstract class in Java?

   • Answer: An interface can only have abstract methods (before Java 8) and constants. An abstract class can have both abstract and concrete methods. A class can implement multiple interfaces but can extend only one abstract class. Interfaces define 'what' to do, abstract classes define 'how' (partially).

4. What are different types of exception handling mechanisms in Java?

   • Answer: Java uses the `try-catch-finally` block for exception handling. `try` encloses the code that might throw an exception, `catch` handles specific exceptions, and `finally` executes regardless of whether an exception occurred. Custom exceptions can also be created by extending the `Exception` class.

5. Explain the concept of garbage collection in Java.

   • Answer: Garbage collection is the automatic process of reclaiming memory occupied by objects that are no longer reachable by the program. It prevents memory leaks and simplifies memory management.

6. What is the difference between HashSet and TreeSet?

   • Answer: HashSet stores elements in a hash table, providing fast add, remove, and contains operations (O(1) on average). TreeSet stores elements in a sorted order using a tree structure (Red-Black tree), offering slower add/remove operations (O(log n)) but efficient retrieval of elements in sorted order.

7. What is the difference between ArrayList and LinkedList?

   • Answer: ArrayList uses an array to store elements, providing fast random access (O(1)) but slower insertion/deletion (O(n)). LinkedList uses a doubly linked list, offering fast insertion/deletion (O(1)) but slower random access (O(n)).

8. Explain the concept of multithreading in Java.

   • Answer: Multithreading allows multiple threads to execute concurrently within a single program, improving performance and responsiveness. Threads share the same memory space but have their own call stack.

9. What is the purpose of the `synchronized` keyword in Java?

   • Answer: The `synchronized` keyword provides thread synchronization, ensuring that only one thread can access a critical section of code at a time. It helps prevent race conditions.

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