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Java interview questions

15 Helpful Java Interview Questions

Public speaker Stephen Keague once said, “proper preparation prevents poor performance.” This can applied to many different things, especially when prepping for Java interview questions.
As a job hunter or a career switcher, you should always be prepared for a job interview. Remember that hiring managers play the most critical role in the hiring process. So if you’re a new Java developer eager to get that dream job or an experienced developer applying for a better job and compensation, you have to impress the hiring manager by acing the interview.
There are three critical phases in an interview; the first one is the invitation, the second is the meeting, and the third is the follow-up.

Three steps of a job interview


Phase I: The Invitation

Interviewing all applicants one by one is a very tedious job, so hiring managers try to review each candidates’ resume meticulously. If they think you are qualified for the job, you will get an invitation for the second phase of the interview.
A carefully and professionally written resume will give you the advantage to receive an invitation. An invitation is sent through email, phone call, a text message, and sometimes through a letter.

Phase II: The Meeting

Jobs are won and lost during this phase in the interview process because this is the time where you will come face-to-face with the hiring manager. The primary goal of this meeting is for the hiring manager to assess your capabilities and discern your personality.
The first impression you show during this phase in the interview will make or break your chance to get hired, so after getting an invitation, it’s best to prepare for this phase in the interview process.

Phase III: The Follow-Up

Follow-up is as vital as the first two phases. Waiting can be the most exhausting part, but it doesn’t have to be that way. Waiting for that most-awaited phone call when there is no guarantee that it will come is one mistake job applicants often make. So, to avoid a painful bout of waiting, you should call and ask if you made the cut a few days after your interview.

Java Interview Questions

A job interview benefits both the employer and the applicant. Aside from showcasing your skills and abilities, it helps you connect with your future employer and allows them see that you meet their expectations. From the interviewer side, they get to know a candidate beyond what’s written on a resume, therefore, making it easier for them to make effective and efficient hiring decisions.
Below are some examples of technical Java interview questions with their sample answers:

1. What is Java?

Java is one of the general-purpose programming languages that was developed by James Gosling at Sun Microsystems. It was designed to make electronic devices communicate with each other.

2. What are JVM, JRE, and JDK?

Java Virtual Machine (JVM) enables a computer to run Java programs and other languages that are compiled to Java bytecodes. Java Runtime Environment (JRE) is a set of software tools that combine Java Virtual Machine, platform core classes and supporting libraries. Java Development Kit (JDK) is a software development environment that includes JRE, a compiler (javac), a documentation generator (Javadoc), an archiver(jar), an interpreter/loader (java), and other tools used for developing Java applications and applets.

3. What is the thread life cycle in Java?


The new state is the state when we create a new thread object using a new operator. The start() method is not yet invoked during this time, so the thread is not considered alive.


After the invocation of the start () method, the thread becomes runnable. Depending on the OS implementation of the thread scheduler, the thread can run instantly or be kept in the runnable pool before running.


After the thread scheduler selects the thread and executes the run () method, the thread becomes a running state.


The thread is still alive but is not permitted to run.


Once the thread finished executing, its state is changed to dead, and it’s considered to be not alive.

4. Why is Java not 100% Object-oriented?

Java is not 100% Object-oriented because it uses Primitive Data types like boolean, byte, char, short, int, long, float and double which are not objects.

5. What is Heap and Stack Memory?

Stack Memory is temporary storage of variables that are created by each function in a special region of your computer’s memory which is optimized and managed by the CPU. Heap is a free-floating region of your computer’s memory and is larger than the stack memory. It’s a region in your computer’s memory that is not as tightly handled by the CPU.

6. What are the supported platforms by Java Programming Language?

There are several platforms supported by Java: Mac OS, Windows and various versions of UNIX/Linux like HP-Unix, Sun Solaris, Redhat Linux, Ubuntu, CentOS, etc.

7. What do you mean by Multithreaded program?

A thread is a placeholder for the capacity of a central processing unit (CPU)  to manage multiple requests simultaneously is called multithreading.

8. How did Java enable high performance?

Java enabled high performance by introducing JIT- Just In Time compiler. JIT helps the compiler to compile the code On demand basis, i.e., whichever method is called only that method block will get compiled making compilation fast and time-efficient. This makes the java delivering high performance.

9. What do you mean by Access Modifier?

Access modifiers, sometimes called the access specifiers, are keywords in object-oriented languages that specify the accessibility of a given class, fields, constructors, and methods. There are four different Java Access Modifiers: private, default (package), protected, and public.

10. What are Serialization and Deserialization?

Serialization is a process of converting/writing an object into a sequence of bytes. The reverse process of creating an object from a sequence of bytes is called deserialization.

11. What is Network Programming?

Network Programming indicates writing programs that execute across multiple devices like computers, in which the devices are all connected using a network.

12. What are the Packages in Java?

A package is a group of interfaces, classes, and other packages. A package is convenient because of its reusability, it’s used for regrouping large Java projects to have better organization, and it’s used to avoid name collisions and thus avoid conflicts. There are two types of packages in Java: the built-in package and the user-defined package.

13. What is File Class and what are its uses?

The abstract representation of file and directory structure is called a file class. It has a mechanism that can delete, create, and modify file attribute.

14, What is the Java Collections API?

Collections are used to store groups of objects. The Collections API provides several interfaces (including Collection, List, Map, and Set) to define a standard way of using a range of concrete data structures. The interfaces and classes of the Collections API belong to the java.util package.

15. What is Constructor Chaining?

The method of invoking one constructor from another, whether it’s within the same class or from the base class, is called constructor chaining. Constructor chaining occurs through inheritance or legacy.
Aside from researching about interview questions, there are also other things you can do as you prepare for the job interview: analyze the job description, make a match of your skill and their requirements, research about the company, practice interviewing, prepare proper clothes, study and practice interview etiquette then learn how to listen and ask questions during the interview.

hands of three different people during a java coding interview

Coding Dojo Career Support

Java is just one of the several top programming languages offered at Coding Dojo. Java 8, JSP, SpringMVC, MySQL, (JPA) Hibernate, JUnit, ThymeLeaf, Tomcat, and JVM are the technologies we teach together with the topics MVC Framework, ORM, SQL, JPQL, Test-driven Development, Dependency Injection and Inversion of Control, Authentication/Login, and Application Deployment. Alongside Java, MEAN, RUBY, C#/.NET, and Python are also part of our curriculum.
Besides our coding bootcamps, Coding Dojo also offers career services to help alumni achieve their long-term and short-term career goals and help students build their career. Part of this career service is a one-on-one discussion with a career advisor who will give you feedback and support on career-related projects to elevate your job prospect. Another part of this career service is the access to a workshop where you can learn behavioral interview techniques, networking and pay negotiation.
Many of our alumni don’t have a coding background before they joined the bootcamp, but thanks to our curriculum and career services, 91 percent of our alumni land a full-time job a year after graduation at tech companies like Google, Amazon, Facebook and Microsoft.