Java interview questions along with brief answers

1. What is the difference between == and .equals() in Java?
- == compares object references, while .equals() compares the content of objects.

2. Explain the difference between ArrayList and LinkedList.
- ArrayList uses a dynamic array to store elements, providing fast random access. LinkedList uses a doubly-linked list, offering efficient insertion and deletion.

3. What is the significance of the static keyword in Java?
- The static keyword is used to create variables and methods that belong to the class rather than instances of the class. These can be accessed without creating an object.

4. What is the difference between an abstract class and an interface?
- An abstract class can have both abstract (unimplemented) and concrete (implemented) methods, while an interface can only have abstract methods. A class can implement multiple interfaces, but it can extend only one abstract class.

5. What is the purpose of the finally block in exception handling?
- The finally block is used to ensure that a specific block of code is always executed, regardless of whether an exception is thrown or not.

6. Explain the concept of multithreading in Java.
- Multithreading is the concurrent execution of two or more threads. Threads allow programs to run tasks in parallel, improving performance. In Java, you can create threads by extending the Thread class or implementing the Runnable interface.

7. What is the NullPointerException and how can it be avoided?
- NullPointerException occurs when you try to access a method or field of an object that is null. To avoid it, ensure that objects are properly initialized before accessing their members.

8. How does garbage collection work in Java?
- Garbage collection is the process of automatically reclaiming memory occupied by unreferenced objects. Java uses a garbage collector to identify and delete objects that are no longer reachable.

9. Explain the final keyword in Java.
- The final keyword can be applied to variables, methods, and classes. When applied to a variable, it means the variable's value cannot be changed. When applied to a method, it prevents method overriding. When applied to a class, it prevents the class from being subclassed.

10. What is the Java Virtual Machine (JVM)?
- JVM is a virtual machine that executes Java bytecode. It abstracts the hardware and operating system details, allowing Java programs to run on any device with a compatible JVM.

These questions cover a range of Java concepts commonly discussed in interviews. Be prepared to elaborate on your answers and provide examples if requested during an interview.

Key Differences Between Java and C#

1. Java is a great option for building complex web-based, highly concurrent applications, whereas C# is ideal for game development and mobile development.
2. Java requires Java Development Kit, which includes a Java compiler and runs a time environment to run Java on any machine, whereas C# libraries are being shipped with a .NET framework with IDE like Visual Studio.
3. Source code written in Java is compiled into bytecode, and then bytecode is converted to machine code, ready to run on any platform, whereas with C#, a code is interpreted into bytecode (MSIL) which is compiled by CLR and JIT compiler will convert MSIL into native machine code.
4. Java is designed to execute on JRE (Java Runtime Environment), whereas C# is designed to execute on CLR (Common Language Runtime).
5. Java is heavily used for building a complex application in an open-source ecosystem, whereas C# is mostly used to develop an application for Microsoft platforms.
6. Java provides a clear difference between Checked and Unchecked exceptions, whereas the C# approach is minimalistic in nature by choosing only one type of exception.
7. Java enables the polymorphism by default, whereas with C#, one must invoke the “virtual” keyword in base-class and “override” keyword in a derived class.
8. Java library ecosystem is vast and well documented, which further assist in developing functionality at a decent pace, whereas C# libraries work within the Microsoft ecosystem, which is limited as compared to Java.
9. Java has traditionally a huge community providing open-source libraries, so any need can be fulfilled with the libraries, whereas free quality libraries support from the Microsoft community is a downside for C#.
10. Generic feature support in Java is compiler-assisted, implemented using erasures, whereas C# takes generics further by integrating them into the CLI and allow type information to be available at runtime.

🔰 JavaScript Roadmap for Beginners 2025
├── 🧠 What is JavaScript & How It Works in Browsers
├── 📄 Adding JavaScript to HTML (Script Tag, External Files)
├── 📝 Variables (var, let, const)
├── 🔢 Data Types & Type Conversion
├── 🔁 Operators (Arithmetic, Comparison, Logical)
├── 🔄 Conditional Statements (if, else, switch)
├── 🔁 Loops (for, while, do...while)
├── 🧩 Functions (Regular, Arrow Functions, Callbacks)
├── 🧱 Arrays & Array Methods (map, filter, reduce, etc.)
├── 📦 Objects & Object Methods
├── 📜 String Manipulation
├── 📅 Date & Time in JavaScript
├── ⚙️ The DOM (Document Object Model)
├── 🎯 Event Handling
├── ⌛ Async JS (setTimeout, setInterval, Promises)
├── 🌐 Fetch API & JSON
├── 📦 ES6+ Concepts (Destructuring, Spread, Rest, Modules)
├── 🧪 Mini Projects (To-Do List, Calculator, Weather App)

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👉 1. Review your technical skills: Make sure you know the programming languages and tools that are relevant to the job you're applying for. Brush up on HTML, CSS, JavaScript, and any other programming languages you plan to use.

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3. Days 8-10: Understand functions, how to create them, and pass parameters.
4. Days 11-14: Dive into arrays and how to manipulate them.

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5. Days 15-17: Learn about pointers and their role in C programming.
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Throughout the 30 days, make sure to:
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