Indeed states the average salary for a java developer as $100,249 per year in the United States, and the average hourly salary as $64.27.

With this sweet head start, we can now shed some light on the profile and draw an outline of the commonly asked Java developer interview questions.

Java is the core requirement among developers because of its uncomplicated syntax and acceptance over multiple operating systems.

Today, with over 10 million developers using Java language, employers are quite determined to hire professionals with intricate knowledge of coding and designing to deploy various diversified applications.

This blog recapitulates 30 essential Java developer interview questions in 2021 to help you prepare well and land your dream job.

Listed below are the three sections in this blog as per seniority level:

Cracking an interview is not an easy task, but with Hiration’s Interview Preparation and its in-house panel of industry experts, we are here to prepare you for all levels of Java interview questions.

Featuring the 5 commonly asked senior Java developer interview questions answered in this blog:

Entry Level Java Developer Interview Questions

In this section, we will cover junior Java developer interview questions with 10 java developer interview questions and answers and 10 entry-level Java developer interview questions.

Why is the Java platform independent?

Java is a platform-independent language because the programs compiled in it are in bytecode which can run on any system irrespective of the underlying operating system.

Explain the importance of public static void main(string args) in Java.

The main() method in Java is the beginning point for any java program. The syntax used for the main method in Java programming is-:

public static void main(String args[])

As the main method is public and static, it helps Java access it without initializing the class. The value which is passed as an input is an array of String by which runtime arguments are passed.

What are wrapper classes in Java?

It is used to convert the Java primitives into reference types. A dedicated class allotted to every primitive data type is called wrapper classes as they wrap the primitive data type into an object of that class.

Why are pointers not used in Java?

Java does not use pointers because they increase the complexity of the program. Since Java is known for its simple code, adding the concept of pointers will be contradicting. Also, since JVM is responsible for implicit memory allocation, in order to avoid direct access to memory by the user, pointers are discouraged in Java as they can make the program unsafe.

What is a JIT compiler and how does it work?

Just-In-Time compiler is a program in Java that converts byte code into instructions for the processor. Whenever a Java method is invoked, the JIT compiler is by default initiated. It then converts the compiled byte code into native machine code. Once the method has been compiled, the JVM summons the compiled code of that method directly, resulting in performance optimization.

Define a Java Class.

A class in Java is the blueprint containing all data like variables and methods to describe the behavior of an object.

Define constructor chaining.

Constructor chaining is the process of calling one constructor from another with regard to the current object. It is possible only where a subclass constructor is responsible for invoking the superclass constructor first. There could be any number of classes in the constructor chain.

What is a Map in Java?

A map is an interface of a utility package that maps unique keys to values. It is not a subset of the main interface, thus it behaves differently from the other collection types.

What is a composition in Java?

Composition is a design technique to implement a has-a relationship. Inheritance is used for code reuse purposes and the same can be done using composition. Composition is a way of describing reference between two or more classes using instance variables and an instance should be created before it is used.

What is the Java Reflection API?

It provides the ability to inspect and modify the behavior of any application during execution. Reflection provides information about the class to which an object belongs and the methods of that class that can be executed by using the object.

collection-framework-hierarchy

Source: Edureka

10 Entry Level Java Developer Interview Questions

Previously discussed questions cover the basics of Java and the questions below are an extension to them. These are the frequently asked Java interview questions for freshers:

  • Explain JDK, JRE, and JVM?
  • Is Java a statically or dynamically typed language?
  • How do you organize your class modules and assets?
  • Why is Java not 100% Object-oriented?
  • What are the differences between Heap and Stack Memory?
  • What is the difference between equals () and == ?
  • What do you understand about the term ‘Functional testing’?
  • What is a singleton class in Java and how can we make a class singleton?
  • What is the difference between an Array list and vector in Java?
  • What is a package in Java? List down various advantages of packages.

Mid Level Java Developer Interview Questions

An intermediary profile requires a median of skills and experience. Therefore, we have curated a set of pointers on Java developer interview questions for 5 years experience (flexible) profile:

  • Focus on design patterns and prepare 3-4 patterns in the best way that you can. Share your past project experiences as real-life examples are always a hit.
  • Learn each and every detail such as system design, modules design, and database structure of your recent projects. Keep everything at your fingertips.
  • Practice multi-threading, especially executors and thread pools. Create some programs on paper to present as samples.
  • Practice some complex SQL queries and study joins, indexes, and their syntax.
  • You must be thorough with your OOP concepts.

Java Senior Developer Interview Questions

Stated below are the 10 most commonly asked Java interview questions for a senior developer:

Which methodologies can be used to write unit tests?

JUnit is the renowned unit-testing framework in the Java ecosystem. Based on the Java 8 version, many new features have been added in the JUnit 5.

Define how Java SE is related to Java EE?

Java Enterprise Edition (Java EE) is a Java-centric environment for building, developing, and deploying web-based enterprise applications online. Java EE includes some major components of the Java Standard Edition (Java SE).

Can we have an empty catch block?

Yes, we can have an empty catch block in Java, though this is not a very preferable practice. Generally, the code in the try block is capable of producing exceptions, and if anything goes south, the catch block handles the exception.

Does Spring Bean provide thread safety?

Spring bean consists of one instance per context because its default scope is a singleton. That means having a class-level variable that any thread can update, will lead to inconsistent data. Thus, in default mode, spring beans are not thread-safe.

Define Marker Interface.

It is a design pattern used to provide run-time information about the objects. It delivers external means to add metadata with a class where language does not have any explicit support for metadata. The most common examples of marker interfaces in Java are Serializable, Cloneable, etc.

What is object cloning in Java?

It is the process of creating an exact copy (clone) of an object. This method creates a new instance of the class of the current object, then initializes all its fields with the same contents of corresponding fields.

What is controller in Spring MVC framework?

Controllers provide access to the behavior of an application using a service interface. It interprets user input to transform into a model represented to the user by the view. Spring MVC implements the controller in a way that enables you to create a wide variety of controllers.

State the difference between fail-fast and fail-safe?

All the collection classes in the Java Utility package are fail-fast, while the collection classes in Java Utility concurrent are fail-safe. The fail-safe property works with the clone of the underlying collection and thus, it is not affected by any modification in the collection. Whereas, the fail-fast iterators.

Which Swing methods are thread-safe?

There are only three thread-safe methods: repaint, revalidate and invalidate.

Is Java “pass-by-reference” or “pass-by-value”?

Java is always pass-by-value. Unfortunately, when we pass the value of an object, we are passing the reference to it. There is no such thing as "pass-by-reference" in Java. This is confusing to beginners.

Few more Java Interview Questions for Senior Developer are as follows:

  • How does Garbage Collection prevent a Java application from going out of memory?
  • Servlets 3.0 introduced async support. Describe a use case for it.
  • Why do you think lambda expressions are considered significant for Java 8?
  • Why would it be pointless for a static or final method to use dynamic binding?
  • What will happen if you put System. exit(0) on a try or catch block? Will the block execute finally?

Key Takeaways

  • The average hourly salary as of a java developer is $64.27 in the United States.
  • Java developers need a variety of skills, from a thorough knowledge of the basics to an understanding of the latest developments and the execution process.
  • Some of the basics of Java which you need to have a firm grasp on are: Core Java, Servlets and JSP, and Frameworks.
  • While applying for an intermediary profile, make sure to deliver your past project experiences and how you have worked your way in the Java ecosystem.
  • Some of the advanced concepts you must familiarise yourself with while applying for senior profiles are AI and Machine Learning, Blockchain, Python, and Advanced JavaScript Framework.

These questions will definitely help you draw an outline of all concepts you need to work upon as per your seniority level.

In case you require structured guidance, Hiration’s Interview Preparation is the right place for you with our experts equipped with all questions and answers as per your niche.