Developer interview question answer for fresher

1. What is Java and why is it platform-independent?

   
   Java is a high-level, object-oriented programming language designed to be platform-independent by compiling source code into bytecode, which runs on any machine with a Java Virtual Machine (JVM). This "write once, run anywhere" capability is one of its core strengths.

2. Explain OOP principles in Java.

   
   Java supports four key OOP principles:

• Encapsulation: Bundling data and methods in a class, restricting access via access modifiers.

• Inheritance: Creating new classes from existing ones to reuse code.

• Polymorphism: Ability to perform different actions through the same interface, typically method overriding and overloading.

• Abstraction: Hiding complex implementation details and showing only essential features.

3. Difference between String, StringBuilder, and StringBuffer?

• String is immutable; every modification creates a new object.

• StringBuilder is mutable but not thread-safe, suitable for single-thread use.

• StringBuffer is mutable and thread-safe, designed for concurrent use.

4. What is the difference between an Abstract class and an Interface?

• Abstract classes can have method implementations and state (fields), supporting code reuse.

• Interfaces can only have abstract methods (until Java 8 introduced default and static methods) and define a contract without state.

• A class can implement multiple interfaces but inherit only one abstract class.

5. Explain Exception Handling in Java

   
   Java uses try-catch-finally blocks to handle exceptions. Checked exceptions must be declared or handled, while unchecked exceptions (runtime exceptions) do not require declaration. Finally executes regardless of exceptions to free resources.

6. What are Java 8 features you have used?

   
   Common features include Lambda expressions for functional programming, Streams API for working with collections in a declarative way, and default methods in interfaces for backward compatibility

7. What is multithreading and how do you create a thread in Java?

   
   Multithreading allows concurrent execution of two or more threads. You can create a thread by extending the Thread class or implementing the Runnable interface. Thread lifecycle states include New, Runnable, Running, Waiting, and Terminated.

8. How does Spring handle Dependency Injection?

   
   Spring’s DI framework manages object creation and injection using annotations like @Autowired or through XML configuration, promoting loose coupling by injecting dependencies rather than creating them internally.

9. What is the difference between HashMap and TreeMap?

   
   HashMap uses hashing and offers constant-time O(1) average complexity for get/put operations but does not maintain order. TreeMap is a Red-Black tree implementation, offering O(log n) complexity and sorts keys in natural order or by a comparator.

10. Explain the concept of Garbage Collection in Java.

    
    Garbage Collection automatically reclaims memory by removing unused objects. The JVM manages this through various algorithms like Mark-and-Sweep, Generational GC, and provides tuning options for performance optimization.

These answers reflect in-depth understanding expected of Java Developers, encompassing core language knowledge, design principles, popular frameworks, and Java's evolving features. Including examples from personal projects or previous roles will strengthen responses in your interview.