Java developer Junior job interview FAQ: part 1

Java is a popular programming language used to develop various kinds of applications. If you’re going to interview for a Java developer job, it’s important to be well prepared and be able to answer frequently asked questions. Your answers should be concise, but at the same time rich in information, and this way you can show your potential employer that you are professionally prepared for the interview.

In the first part of this series, we’ll look at common key questions aimed theoretically at the junior Java developer position that employers tend to ask on 1. round of job interviews.

See also other articles from the Java developer interview series:

What is Java?

Java is a high-level object-oriented programming language designed to be platform-independent, which means that code written in Java can run on any system that has a Java Virtual Machine (JVM) installed.

One of the key advantages of Java is its “write once, run anywhere” philosophy, which allows developers to create code that can be used on different platforms without the need to modify it for each individual system. Java is also known for its robustness, security features, and large library of standard classes and methods that facilitate the development of complex applications.

JDK, JRE and JVM – what is the difference?

JDK (Java Development Kit) is a software development tool that developers use to create Java applications. It includes tools such as a compiler, debugger, and other utilities needed to create Java applications.

JRE (Java Runtime Environment) je softvérový balík, ktorý je potrebný na spustenie Java aplikácií. It includes tools such as a compiler, debugger, and other utilities needed to create Java applications.

JVM (Java Virtual Machine) is a software engine that is responsible for executing Java bytecode. The JVM interprets the compiled Java code and executes it on the target machine. It provides a layer of abstraction between Java code and hardware, making Java programs platform-independent.

Explain the concept of Object Oriented Programming

Object-oriented programming (OOP) is a programming paradigm that focuses on modeling real-world things in a programming language using objects. In OOP, code is organized into classes and objects. Classes define the properties and behavior of objects that are created from these classes. Objects can interact with other objects to create more complex systems.

OOP has several major benefits, such as code reuse, simplified code management and maintenance, the ability to model complex processes, and the ability to perform abstraction. Therefore, OOP is very popular nowadays and is widely used in various fields, including web applications, mobile applications, and games.

List the key features of Java

Platform independence: the Java code can be compiled once and run on any operating system.

Object-oriented: Java is an object-oriented programming language, which means that it allows you to create objects and define their properties and methods.

Simplicity: Java is designed as a simple language with an easy-to-learn syntax, making it accessible to beginners.

Robustness: Java has a strong memory management system, automatic garbage collection and exception handling, making it a robust language.

Security: Java provides built-in security features such as class loaders, bytecode validation, and a security manager, making it a secure language.

Portability: Java programs can run on any operating system on which the Java Virtual Machine (JVM) is installed.

Multithreading: Java supports multithreading, which allows programs to perform multiple tasks at the same time.

High performance: the Just-In-Time (JIT) compiler and an efficient memory management system make Java a high-performance language.

Dynamicity: Java supports dynamic class loading, which allows developers to load classes only when they are needed.

Distributability: Java provides built-in support for distributed computing, allowing applications to communicate over a network.

What is the difference between primitive data types and objects?

There are two types of data in Java: primitive and reference (objects). The main difference between the two is that primitive data types are basic data types built into the language, while objects are instances of classes.

Primitive data types include integer types (byte, short, int, long), floating-point types (float, double), boolean types (boolean), and character types (char). These types are used to store simple values directly in memory and are transmitted by value.

Objects, on the other hand, are created from classes and stored in memory as references to their locations. Objects can store complex data structures and can have methods and properties associated with them. They are passed by reference, which means that when you pass an object to a method, the method receives a reference to the object’s location in memory.

Another difference between primitive data types and objects is that primitive data types have a fixed size and can never be null, while objects can be null and have different sizes based on the data they contain.

What is a Java class?

Java class is a template for creating objects. Defines the properties (or attributes) and behaviors (or methods) that an object of this class will have.

A class can have one or more constructors (java constructor), which are special methods that are called when creating an object of that class. The constructor initializes the attributes of an object to specific values.

In Java, classes are declared using the class keyword followed by the class name. The class body is enclosed in compound parentheses and contains the attributes and methods of the class.

Classes are the basis of object-oriented programming in Java. They allow the creation of objects that can perform specific tasks and interact with other objects in a predictable way.

If you are a complete beginner, click on the article How to become a developer. Read more about the Java developer’s salary. Are you looking for a job as a senior Java developer or junior Java developer? Check out our employee benefits and respond to job offers.

About the author

Jozef Wagner

Java Developer Senior

Viac ako 10 rokov programujem v Jave, momentálne pracujem v msg life Slovakia ako Java programátor senior a pomáham zákazníkom implementovať ich požiadavky do poistného softvéru Life Factory. Vo voľnom čase si rád oddýchnem v lese, prípadne si zahrám nejakú dobrú počítačovú hru.

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