Interview question and answer for 5-8 year experience for Java developer

1. Explain the difference between String, StringBuilder, and StringBuffer in Java.

   
   Answer: String is immutable, so each modification creates a new object. StringBuilder is mutable and faster but not thread-safe. StringBuffer is thread-safe due to synchronization but slower than StringBuilder.

2. What are the four pillars of Object-Oriented Programming (OOP) in Java?

   
   Answer: Encapsulation, Inheritance, Polymorphism, and Abstraction.

3. How do you create a thread in Java? What are the ways to create threads?

   
   Answer: Threads can be created by extending the Thread class or implementing the Runnable interface. The Runnable interface is preferred for better resource management and flexibility.

4. Explain synchronization and deadlock in Java. How do you avoid deadlocks?
   Answer: Synchronization prevents concurrent access issues by allowing one thread at a time. Deadlock occurs when two or more threads wait indefinitely for resources held by each other. Deadlocks are avoided by proper resource ordering and timeout mechanisms.

5. What is the difference between checked and unchecked exceptions?

   
   Answer: Checked exceptions are checked at compile time and must be handled or declared, like IOException. Unchecked exceptions are runtime exceptions, like NullPointerException, and do not require explicit handling.

6. How does HashMap work internally?

   
   Answer: HashMap uses an array of buckets and a linked list (or balanced tree if many collisions) in each bucket. It computes the hashcode of the key, maps it to a bucket index, and stores key-value pairs.

7. Explain method overloading vs method overriding.

   
   Answer: Overloading allows multiple methods with the same name but different parameters in the same class. Overriding means redefining a superclass method in the subclass with the same signature.

8. What are design patterns you have used, and which ones do you prefer?
   Answer: Common patterns include Singleton, Factory, Observer, and Decorator. Preference depends on the problem—Singleton for global access, Factory to abstract object creation, etc.

9. What improvements did Java 8 introduce? How do you use lambda expressions?

   
   Answer: Java 8 introduced lambda expressions, functional interfaces, Stream API, default and static methods in interfaces. Lambda expressions provide concise syntax for implementing functional interfaces.

10. How do you handle performance issues and optimize Java applications?
    Answer: Use profiling tools to identify bottlenecks, optimize algorithms, use efficient data structures, minimize synchronization overhead, and tune JVM parameters for garbage collection.

These questions reflect typical expectations for a Java developer with 5-8 years of experience, focusing on practical knowledge, coding ability, and architectural understanding. Preparing detailed, experience-based responses will help demonstrate expertise. This covers both conceptual and practical aspects relevant to the role and career stage.