Entry level Java Junior Dev Technical Interview Questions (and answers).

What is a Constructor?

A Block of code responsible for building/initializing your object(s).

What is a Java Class?

A Java class is the blueprint of an object, within Java.

Explain what a bean is within the Spring Framework.

A bean is just an object that was created via dependency injection.

What is the difference between a Function and a Method?

A function is a piece of code that can be called by name and does NOT need to be within a class to run, a Method can also be called by name but only associated with the object. Methods are commonly used with Java and Functions are primarily used with JavaScript.

What are the pros and cons of using Maps?

A major advantage of using a HashMap is to achieve close efficiency for search and delete operation, efficiency for add operation. A disadvantage is the rehashing operation is a costly operation in terms of run-time efficiency.

What is a final method?

A method that can NOT be over-written by a sub-class. It can only be used one way.

What is absraction?

Abstraction hides complexity in the program to focus on the front issues.

What is Object Oriented Programming?

Also known as OOP, it is a programing paradigm based on the concept of 'objects', which can contain data and code.

What is the difference between an Error and an Exception?

An Error can not be caught by the application and is serious. An Exception may have been expected by the application, and can easily be dealt with.

What is an Event?

An event is a signal received by a program from the operating system as a result of some action taken by the user.

What is the difference between an interface and an abstract class?

An interface can only hold abstract code, but you can implement multiple interfaces. An abstract class can hold both concrete and abstract code, but you can only extend ONE abstract class.

How do you create an instance of a Class?

By building/creating a constructor within your class.

How do you communicate between two classes?

By implementing an Interface.

What is CD/CI?

CD : Continuous Delivery - is a software development methodology where the release process is automated CI: Continuous Integration - is a software development practice where members of a team use a version control system and frequently integrate their work to the same location, such as a main branch.

What is Cloud Development?

Cloud Development is developing applications that are served on the cloud. (We did not cover this at all in WCCI).

What is DOM/DOM Manipulation?

DOM - Document Object Model. DOM Manipulation will allow programs and scripts to dynamically access and update the content, structure and style of documents client side.

What is dependency injection?

Dependency injection is a pattern where a class gets an instance of an object needed from an external source.

What is Encapsulation?

Encapsulation is accomplished when each object maintains a private state, inside a class.

What is a Final Variable?

Final variable is just a constant variable. It can not be changed once instantiated (sometimes written with upper-case to signal it is final).

What is the difference between Float and Double?

Float represents 7 digits of accuracy, Double is 15. (Double is essentially Float +1).

What is inheritance?

Inheriting features from a similar or the same method or class.

What is the purpose of an H2 Database?

It allows the storage of data within memory and not on disk. This allows easy access and retrieval, however the downside is that an H2 Database is NOT persistent.

What is the latest version of Java? (????)

Java 8 is the current latest version released out to the public for general use, Java 16 (or JDK 16) is the most current version for developers to use.

What is JPA?

Java Persistant API - is a specification of Java which is used to access, manage, and persist data between Java object and relational database.

Give an example of a weakly typed programming language.

JavaScript

What is JSON?

JavaScript Object Notation. commonly used for transmitting data in web applications

What is MVC?

MVC stands for Model-View-Controller that is a pattern for implementing user interfaces. The Model describes the business logic independent of the user interface. The view can be any output representation of information. The controller accepts input and converts that input into commands regarding the model or view.

Explain Method Overloading

Method overloading is when you have one class, with multiple methods of the same name but with different arguments.

What is ORM?

Object, Relationship, Mapping. - ManyToMany, OneToMany ect.

What is a Controller?

Part of and MVC application, the controller is responsible for connecting the user with the system/data.

What is polymorphism?

Polymorphism gives multiple methods a way to be called by the class but be given a different 'shape'.

What is the difference between Public, Private, Default, and Protected.

Public is accessible from anywhere, Private is not accessible outside of the object scope, Default is accessible from anywhere as long as it is within the same package, Protected is accessible from the object as well as the sub-class of the object(s).

Explain Scope

Scope describes the variables only accessible inside the region they've been created.

What is the difference between Spring and Spring Boot?

Spring is a Java framework that provides infrastructure support for developing applications. Spring Boot is an extension of the Spring framework, that eliminates the boilerplate configurations for setting up a Spring application.

Why would you use Spring framework?

Using the Spring framework will speed up development time by defining many defaults for you. Very useful for developing MVC applications.

Can you have multiple inheritances?

Yes, but only very specific types, used through interfacing in order to implement onto a class.

Can you have more than one Main Method?

Yes, you can have more than one main method but different signature. This is known as Method Overloading.

How do you find the length of a String in Java?

You use the string.length() method.

What is an Object?

a runtime entity that contains data and responds to messages.

What is agile methodology?

a type of project management process where demands and solutions evolve through the collaborative effort of the developers and their customer(s)/clients.

What is a REST or RESTful API?

an API is an Application Programming Interface, a REST API allows for interaction with RESTful web services (for example the Get, Post, Pull, Delete).

What is a Conditional?

an if-then statement/used to control the flow of the program.

What is the difference between an Array and an ArrayList?

and Array is a linear data structure providing functionality to add elements in a continuous manner, an ArrayList is a Collection.

How do you find a specific character in a String?

use the charAt() method.

What are advantages/disadvantages of using Strongly types vs Weakly typed languages?

Strongly typed languages have less room for error, where as weakly typed languages must rely on user input in order to find errors.

Explain TDD?

TDD ( Test Driven Development) - write tests with failing, then make methods for them to pass.

What is DNS?

The Domain Name System (DNS) converts domain names or host names into IP addresses.

What is the difference between JDK and JRE?

The Java Runtime Environment (JRE) is basically the Java Virtual Machine (JVM) where your Java programs are being executed. It also includes browser plugins for applet execution. The Java Development Kit (JDK) is the full featured Software Development Kit for Java, including the JRE, the compilers and tools (like JavaDoc, and Java Debugger), in order for a user to develop, compile and execute Java applications.