Interview Questions JavaScript Part 1

Basic Java

1. What is Java?

Java is a high-level, object-oriented programming language developed by Sun Microsystems (now owned by Oracle). It is designed to be platform-independent, which means that Java programs can run on different types of computers without modification. This is achieved through the use of the Java Virtual Machine (JVM).

2. What are the main features of Java?

- Object-Oriented: Everything in Java is an object.

- Platform-Independent: Java code is compiled into bytecode that can run on any system that has a JVM.

- Simple and Easy to Learn: Java syntax is clean and easy to understand.

- Secure: Java has built-in security features that help protect applications from threats.

- Robust: Java has strong memory management and exception handling.

- Multithreaded: Java supports multithreading and concurrency.

- High Performance: Java's performance is enhanced through Just-In-Time (JIT) compilers.

- Distributed: Java has extensive support for distributed computing through tools like RMI and EJB.

3. What is the difference between JDK, JRE, and JVM?

- JDK (Java Development Kit): A full-featured software development kit used to develop Java applications. It includes the JRE, an interpreter/loader (Java), a compiler (javac), an archiver (jar), a documentation generator (Javadoc), and other tools needed for Java development.

- JRE (Java Runtime Environment): Provides libraries, Java Virtual Machine (JVM), and other components to run applications written in Java. It does not include development tools such as compilers and debuggers.

- JVM (Java Virtual Machine): An abstract machine that enables your computer to run a Java program. It converts Java bytecode into machine language.

4. What are the principles of Object-Oriented Programming?

- Encapsulation: Bundling the data (variables) and code (methods) together as a single unit, and restricting the access to some of the object's components.

- Inheritance: A mechanism where one class acquires the properties (methods and fields) of another.

- Polymorphism: The ability of different classes to be treated as instances of the same class through inheritance. It allows methods to do different things based on the object it is acting upon.

- Abstraction: The concept of hiding the complex implementation details and showing only the essential features of the object.

5. What is encapsulation?

Encapsulation is an OOP principle where the data (variables) and the code (methods) that operate on the data are bundled together into a single unit, called an object. This mechanism helps in protecting the data from unauthorized access and misuse. It is achieved by declaring the variables as private and providing public getter and setter methods to access and update the values of private variables.

Advanced Java

6. What is the difference between HashMap and Hashtable?

- Thread Safety: HashMap is not synchronized and is not thread-safe, whereas Hashtable is synchronized and thread-safe.

- Null Values: HashMap allows one null key and multiple null values, whereas Hashtable does not allow any null key or value.

- Performance: Since HashMap is not synchronized, it generally performs better than Hashtable.

- Inheritance: HashMap extends AbstractMap class, while Hashtable extends Dictionary class.

7. What is garbage collection in Java?

Garbage collection is the process of automatically freeing memory by deleting objects that are no longer reachable in a program. It helps in preventing memory leaks by reclaiming the memory used by objects that are no longer in use.

8. Explain the different types of garbage collectors in Java.

- Serial Garbage Collector: Uses a single thread to perform all garbage collection work, which can lead to stop-the-world pauses.

- Parallel Garbage Collector: Also known as the throughput collector, it uses multiple threads to speed up garbage collection.

- CMS (Concurrent Mark-Sweep) Garbage Collector: Aims to minimize pause times by performing most of the work concurrently with the application.

- G1 (Garbage First) Garbage Collector: Divides the heap into regions and performs garbage collection in multiple regions in parallel, prioritizing the regions with the most garbage.

Java Development Tools and Libraries

9. What is Maven and why is it used?

Maven is a build automation tool used primarily for Java projects. It is based on the concept of a project object model (POM) and can manage a project's build, reporting, and documentation from a central piece of information. Maven simplifies the build process, dependency management, and project management by providing a comprehensive and standardized way to handle these tasks.

Best Practices and Problem Solving

10. How do you handle exceptions in Java?

Exceptions in Java are handled using try-catch blocks. You can place the code that might throw an exception within a try block and handle the exception in a catch block. Optionally, a finally block can be used to execute code that needs to run regardless of whether an exception occurs or not. Additionally, custom exceptions can be created to handle specific error conditions.

try {

    // code that may throw an exception

} catch (SpecificExceptionType ex) {

    // handle the specific exception

} catch (AnotherExceptionType ex) {

    // handle another type of exception

} finally {

    // code that will always execute

}