12 Sample Java Interview Questions and Answers

As a web or app developer, you use Java on the server side of many back-end development projects to develop websites, games, and apps. And even though you know Java like your first language, you might still need to answer a variety of Java interview questions to get hired as a developer.

The ability to work with Java is in high demand. In fact, the Bureau of Labor Statistics (BLS) projects a 23% increase in new web developer jobs over the next decades. Additionally, the BLS expects software developer jobs to grow by 25%.

Are you ready to get your answers to the most commonly asked Java interview questions up to code? Read the sample Java interview questions and answers to get started.

12 Sample Java Interview Questions and Answers

1. What Is Java and What Are Its Features?
2. What Is an Object in Java?
3. Walk Me Through the Java Coding Process.
4. What Is a Constructor in Java and How Does It Differ From a Method?
5. How Does Java 8 Compare to Previous Versions?
6. Describe What a Lambda Expression Is and Why It’s Used.
7. Describe the Difference Between Collection and Collections.
8. Describe the Difference Between Arrays and Array Lists.
9. What Is the Difference Between Java and Core Java?
10. Describe the OOPs Concept in Core Java.
11. Why Is the Java Main() Method So Important?
12. Define a Class and Which Variables It Consists Of.
13. What Is the Difference Between a Subclass and Superclass?
14. Compare Strings, String Builders, and String Buffers.

Java Fundamentals Interview Questions

Below, you’ll find questions on basic Java features and functions that every Java programmer or developer should know.

Question #1: What Is Java and What Are Its Features?

This is one of the first Java interview questions you’ll likely encounter. Employers will ask you about your basic knowledge of Java to gauge your overall proficiency and depth of knowledge. You can answer this question by discussing the following:

• A brief overview of Java.
• What Java is used for.
• The key features of Java.

How You Could Answer

“Java is an object-oriented and class-based programming language. It’s used as a server-side language for the back-end development of websites, Android apps, and computer software.

From my experience, Java is one of the easiest programming languages to learn and use. Unlike other programming languages, Java allows developers to create modular programs and reusable code. Plus, it’s platform-independent and easy to use for writing, compiling, and debugging code.”

Question #2: What Is an Object in Java?

If you’re going for any position where you’ll use Java, expect to get interview questions about Java fundamentals like objects. Since Java is an object-oriented programming language, you’ll need to demonstrate your knowledge of objects and their uses.

Here’s what you should include in your answer:

• A definition of an object.
• What objects do.
• How objects are created.

How You Could Answer

“An object is a member of a Java class and is also called an instance. Each Java object contains an identity and state, which get stored in fields as data. It also contains a behavior, which shows up in methods (these are functions in programming languages). Objects are created from classes, which act as blueprints for single and multiple objects.”

Java Coding Interview Questions

The next two Java interview questions and answers will cover your understanding of Java coding, including the coding process and the difference between a constructor and a method.

Question #3: Walk Me Through the Java Coding Process.

If you’re gunning for a programming job, employers will probably ask about your coding process. While your answer should be brief and to the point, it should contain all the steps needed to create a Java program.

Your answer should include details on:

• Writing the code.
• Compiling the code.
• Creating an .h file.
• Method implementation.
• Creating a shared library.
• Running a program.

How You Could Answer

“The steps to creating Java code are simple. First, I write the Java code by creating a class and writing the main program used to create an object. Second, I use a “javac” command prompt to compile the written code. Third, I use the “javah” command to create a header file from a Java class.

In the fourth step, I write the native method implementation and create the .c file to access certain functions and APIs found in other programming languages such as C and C++. Next, I create a shared library with the header and C files created in the third and fourth steps. Lastly, I run the program using a Java interpreter.”

Question #4: What Is a Constructor in Java and How Does It Differ From a Method?

Constructors and methods share some similarities, but they also have some key differences. When asked Java interview questions regarding coding, you should demonstrate your knowledge of constructors and your ability to use them in Java.

Do the following when creating your answer:

• Provide a definition of a constructor and method.
• Describe what they do.
• Explain why they’re used.

How You Could Answer

“Methods are blocks of code in Java that get called upon when new classes emerge. Like methods, constructors are invoked when new classes are created in Java. Constructors also carry the same names as classes and are often used to initialize objects, while methods do not. In addition to constructing objects, constructors assign values to the objects’ members, which are interfaces that contain identifying information.”

Java 8 Interview Questions

Java 8 is a widely used version of the programming language. You may be asked variations of the next two interview questions to demonstrate your proficiency in Java 8.

Question #5: How Does Java 8 Compare to Previous Versions?

As a programmer, you should be proficient in the latest coding platforms, including Java 8. Be prepared to provide a comprehensive answer by studying its features and uses.

Your answer should include these details:

• A description of Java 8.
• What Java 8 does that previous Java versions don’t.

How You Could Answer

“Java 8 is a fairly new version but is not the latest. I have used Java 8 since it was released in 2014 and have found that it works more efficiently for developing and running Java programs than previous versions. This version contains the forEach() method, lambda expressions, Java Stream API, Java Date and Time API, and collection and concurrency API improvements.”

Question #6: Describe What a Lambda Expression Is and Why It’s Used.

A lambda expression is one of the key features of Java 8. In your answer, be sure to provide an overview of what a lambda expression is and how it works.

Here are a few things to include in your answer:

• A brief definition of lambda expression.
• What it does in Java 8.
• Why it’s used.

How You Could Answer

“In Java 8, a lambda expression is a block of code used to define a short function. It allows programmers to use an expression to represent method interfaces in a clear and concise way and functional syntax, which is used to write anonymous methods. It’s also used in collection to filter, iterate, and extract data.”

Java Collections Interview Questions

The next two questions will help you demonstrate your understanding of the collections framework in Java.

Question #7: Describe the Difference Between Collection and Collections.

If you’re trying to land a programming job, expect to answer Java interview questions on collections. Collections and collections frameworks represent objects and are often used for data manipulation.

When comparing collections and collections frameworks, be sure to include:

• A description of both.
• How they’re different.
• What they’re used for.

How You Could Answer

“Collection is a Java interface that represents a group of individual objects as a single unit. However, collections is a utility class that defines utility methods used for collection operations. It’s often used to store, sort, insert, delete, and update data. Unlike Collections, Collection contains a static method, as well as abstract and default methods. Collections only contains static methods.”

Question #8: Describe the Difference Between Arrays and Array Lists.

Both arrays and array lists are data structures in Java. However, they differ in their performance and purpose. When creating an answer to Java interview questions on arrays and array lists, be sure to discuss the following:

• How their performance differs.
• When and why an array or array list is used.

How You Could Answer

“In Java, an array is a container object that holds a fixed set of values in a single variable. They’re often used to store multiple values in a single unit instead of declaring variables separately. An array list is a part of Java’s collection framework and is a resizable array found in the Java.util package. Unlike array, elements can be added or removed from an array list.”

Core Java Interview Questions

Below, you will find two questions regarding Core Java. These sample questions and answers will show you how to differentiate between Java and Core Java, as well as describe the OOPs concept.

Question #9: What Is the Difference Between Java and Core Java?

Core Java is a standard version and subset of the Java programming language. As a programmer, you should demonstrate a clear understanding of both Core Java and Java. Here’s what you should discuss when answering:

• A brief description of both Java and Core Java.
• The purpose of each.
• The features of both.

How You Could Answer

“While Java is a programming language used to create websites and mobile apps, Core Java is a computer platform often used to create server-based and desktop applications. Java consists of three editions: J2ME, J2EE, and J2SE. Core Java only consists of one: J2SE.

Core Java is the most standard version of Java and a subset of the programming language. Additionally, Core Java is based on a single-tier architecture, while Java is based on a two-tier architecture.”

Question #10: Describe the OOPs Concept in Core Java.

Object-oriented programming (OOP) is an integral part of Core Java. When asked Java interview questions regarding OOP, you should provide employers with a detailed overview. Your answer should include a description of:

• How the OOPs concept works.
• Which concepts it comprises.

How You Could Answer

“OOPs is used to improve Java code readability and reusability. It comprises four concepts: abstraction, encapsulation, inheritance, and polymorphism. These four concepts allow developers to create functional methods and variables in Java, then reuse them without jeopardizing their security.”

Java Developer Interview Questions

The remaining questions cover the essentials for Java developers, including the main method, classes, and strings.

Question #11: Why Is the Java Main() Method So Important?

The main() method is essential for web and app development. When asked questions regarding main(), be sure to demonstrate your understanding of the method.

Your answer should include:

• What main() is.
• How main() works.

How You Could Answer

“The main method is the first function for program execution. It directs calls to other program functions and can be assigned to any class. It’s used as an access specifier and identifies the execution point of programs. It also operates on a void function, which means that it doesn’t return any value when it’s finished executing a program.”

Question #12: Define a Class and Which Variables It Consists Of.

A class is always required to write code in Java. Java interview questions on classes are meant to evaluate your knowledge of them, how they’re used, and which variables they include.

Here’s the best way to formulate your answer:

• Describe what a class is and what it does.
• Explain what classes are made up of.
• Describe the variables that make up a class.

How You Could Answer

“A class is a Java template used to create and define objects and methods. The most commonly used classes in Java are array list, final, static, abstract, concrete, and singleton. Classes are made up of static variables, which exist within static keywords in a class. Objects and methods are the other two key components of classes.”

Question #13: What Is the Difference Between a Subclass and Superclass?

Java uses thousands of different classes to create objects and define object data types. Some fall under “subclass” or “superclass.” When answering Java interview questions regarding classes, you should show that you understand the differences between class, subclass, and superclass.

Take the following steps to create your answer:

• Define a subclass and superclass.
• Discuss why subclasses and superclasses are used.
• Describe the differences between the two.

How You Could Answer

“Java uses thousands of different classes, some of which include subclasses and superclasses. Subclasses are classes that are made from superclasses. Subclasses are often used to alter the state and behavior of a superclass. Superclasses are also known as parent classes. To put this into perspective, a superclass could represent ‘transportation,’ while the subclasses derived from the superclass could represent ‘car,’ ‘truck,’ ‘boat,’ or ‘train.’”

Question #14: Compare Strings, String Builders, and String Buffers.

Strings, string builders, and string buffers are used to create or modify character sequences in Java. Each of these serves a different purpose. When formulating an answer to Java interview questions regarding strings, focus on these details:

• A definition of a string, string builder, and string buffer.
• Where and why they’re used.
• Their key differences.

How You Could Answer

“It’s easy to confuse strings, string builders, and string buffers, but they are very different. Strings are sequences of characters that make up objects. A string builder is a class used to create mutable characters. Like strings, string buffers contain sequences of characters. However, the characters found in strings are immutable, which means they can’t be altered or changed.”

Program a Successful Job Search on Monster

At Monster, job searching is basically our second language. After you’ve mastered your responses to these sample Java interview questions, upload your resume on Monster to begin your job search. We’ll get you connected with tons of job recruiters looking for candidates with Java skills. Plus, we offer free notifications when new web or software development jobs become available.