Top 11 Java Interview Questions and Answers

Java is a class-based, object-oriented programming language created to minimize implementation dependencies. It enables developers to write code once and run it anywhere (WORA), meaning that compiled Java code can operate on any platform supporting Java without needing recompilation. Introduced in 1995, Java is widely utilized for developing desktop, web, and mobile applications. Its simplicity, robustness, and security features make it a favored option for enterprise-level applications.

The importance of Java continues to grow because it is an object-oriented language, enabling it to combine “data members” and “data manipulation” effectively. This integration enhances the security of programs and allows them to work seamlessly across various resources and platforms.

In this article we are going to discuss a few possible Java interview questions for both freshers and experienced that can help to crack your interview and to attain your goal by getting the job of your choice.

Java Interview Questions

1) Why is Java a platform independent language?

The Java language was created to be independent of any specific hardware or software. This is achieved because the compiler translates the code into platform-independent bytecode, which can be executed on various systems. The only requirement for running this bytecode is that the machine must have a Java Runtime Environment (JRE) installed.

2) What are the main features of Java?

Java is one of the most popular and widely used languages in the world, offering many features that set it apart from other languages. Here are some of its key advantages:

  • Simple: Java is easy to understand with a straightforward syntax.
  • Platform Independent: Java programs can run on any software and hardware, delivering the same results everywhere.
  • Interpreted and Compiled: Java is both an interpreted and compiler-based language.
  • Robust: Features like garbage collection and exception handling make Java a strong and reliable language.
  • Object-Oriented: Java supports object-oriented programming principles, including classes, objects, and the four pillars of OOP.
  • Secure: Java allows sharing applications without exposing the underlying code, enhancing security.
  • High Performance: Java is faster than many traditional interpreted languages.
  • Dynamic: Java supports dynamic loading of classes and interfaces.
  • Distributed: Java’s distributed nature allows accessing files from any connected machine.
  • Multithreaded: Java can handle multiple tasks simultaneously by defining multiple threads.
  • Architecture Neutral: Java is not dependent on any specific architecture.

3) Can java be said to be the complete object-oriented programming language?

It is accurate to say that Java is a fully object-oriented programming language because everything in Java is encapsulated within classes, and these elements can be accessed by creating objects. However, it is also valid to argue that Java is not entirely object-oriented because it supports primitive data types such as int, float, char, boolean, and double.

So, in response to the question: Is Java a completely object-oriented programming language? We can conclude that Java is not purely object-oriented since it allows direct use of primitive data types, which are not encapsulated within their corresponding wrapper classes.

4) How is Java different from C++?

  • C++ is strictly a compiled language, while Java is both compiled and interpreted.
  • Java programs can run on any machine, unlike C++ programs, which can only run on the machine where they were compiled.
  • C++ permits the use of pointers in the program, whereas Java does not, although Java uses pointers internally.
  • C++ supports multiple inheritance, but Java does not to avoid the complexity and name ambiguity issues associated with the diamond problem. This is one of the most important Java Interview Questions. 

5) Why do we use pointers in C/C++ but not in Java? 

Pointers are complex and potentially unsafe for novice programmers. Java emphasizes code simplicity, and the use of pointers can complicate this. Pointers can lead to potential errors and security issues since they allow direct memory access.

Therefore, Java provides a level of abstraction by excluding pointers. Additionally, using pointers can slow down and complicate garbage collection. Instead, Java uses references, which cannot be manipulated like pointers.

6) What are the four principles of OOP? Explain.

The four principles of OOP are:

Encapsulation: Data Encapsulation is a principle in Object-Oriented Programming that involves concealing data attributes and their behaviors within a single entity.This approach supports developers in maintaining modularity during software development, as it ensures that each object operates independently with its own methods, attributes, and functions. Additionally, it enhances the security of an object’s private properties, effectively achieving data hiding.

Inheritance: Inheritance allows developers to build new classes derived from existing parent classes, enabling them to override or enhance the original properties and methods. This approach is particularly beneficial in large programs with extensive code, as it streamlines maintenance and avoids code repetition. By reusing the parent class’s logic within the child class, developers can create objects that share common code or logic but remain distinct. This method reduces code complexity and eliminates the need to create a unique object for each use case within the program.

Polymorphism: Polymorphism enhances inheritance by enabling objects from different classes to execute methods with the same name but with different implementations. For example, a “show information” method can present diverse details for objects like “car,” “plane,” or “ship.” This principle promotes the development of flexible and modular programs, simplifying the process by allowing common methods and functions to be applied to various object types.

Abstraction: Abstraction enables you to concentrate on the essential elements of a system, ignoring the less critical details that don’t impact its primary functions. This makes programs easier to understand. Abstraction can be seen as an extension of encapsulation. In programs with thousands of lines of code, abstraction ensures that each object only exposes a specific mechanism for interaction, making the internal code mostly independent of other objects. For example, in a movie information program, you can create a “Movie” class that provides access to crucial details like title, release year, and genre, while concealing less important information such as scenes or technical specifics. Learn all these deeply because this is important Java Interview Questions. 

7) What is JVM?

The Java Virtual Machine (JVM) acts as a Java interpreter. It is responsible for loading, verifying, and executing the bytecode generated by Java. While the JVM software varies across different operating systems, it is crucial in ensuring that Java remains platform-independent.

8) What are the memory storages available with JVM?

The JVM includes several memory storage areas:

  • Class (Method) Area: Stores class-level data for each class, including the runtime constant pool, field and method data, and method code.
  • Heap: Allocates memory for and stores objects during runtime.
  • Stack: Holds data and partial results needed for returning method values and performing dynamic linking.
  • Program Counter Register: Keeps the address of the currently executed Java virtual machine instruction.
  • Native Method Stack: Contains all native methods used in the application.

9) Give brief information about the JIT compiler.

JIT, or Just-In-Time, enhances performance during runtime by compiling similar byte code segments simultaneously, reducing compilation time. A compiler translates source code to machine-executable code. The JIT compiler is unique in its process:

First, the Java source code (.java) is converted to byte code (.class) using the javac compiler. The JVM loads these .class files at runtime and converts them to machine code using an interpreter.

The JIT compiler, a component of the JVM, analyzes method calls in the .class files and compiles them into more efficient native code. It optimizes prioritized method calls. After this, the JVM directly executes the optimized code instead of reinterpreting it, boosting performance and execution speed.

10) How JVM, JRE and JDK differ from each other?

JVM: The Java Virtual Machine (JVM) is part of the Java Runtime Environment (JRE) and acts as an interpreter that converts bytecode into machine-readable code. While the JVM itself is platform-dependent, it allows Java bytecode to be platform-independent, enabling Java to run on any operating system. This one is also very important Java Interview Questions. 

JRE: The Java Runtime Environment (JRE) is an installation package that provides the necessary environment to run Java programs or applications on any machine.

JDK: The Java Development Kit (JDK) is a package that offers an environment for developing and executing Java programs. It includes development tools for creating Java programs and the JRE for running them.

11) Define Wrapper class in Java?

A wrapper generally refers to a larger entity that encloses a smaller one. In Java, a wrapper class is an object class that encapsulates primitive data types. Primitive data types are the basic types from which other data types can be derived. For example, integers can form the basis for long, byte, short, etc. In contrast, strings cannot be broken down into simpler types, so they are not considered primitive.

Read More :- What is Colocation? A Beginner’s Guide

Java includes eight wrapper classes: Boolean, Byte, Short, Integer, Character, Long, Float, and Double. Additionally, custom wrapper classes can be created in Java, similar to structures in the C programming language, allowing the creation of custom classes with specific data types. So here are top 20 Java Interview questions. 

We hope this article Java Interview Questions will be helpful enough to attain your goal.

Meenakshi Thakur

Meenakshi Thakur, having 6 Years of Experience in Digital Marketing and Content Writing. I am free to write all types of niche content for websites and blogs. I am passionate about all of the work! I really like to explore the latest tricks in technical areas and develop case studies.

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