Top 39 Java Developer Interview Questions

Important Topics for Java Interviews

There are many topics that can (and should) be covered during Java developer interview questions. Ultimately, it is important to evaluate the needs for your project specifically and ask the ones that are the most meaningful. In fact, we do not recommend asking all of the questions discussed below; rather, we should choose the ones that are the most relevant. In this review, we discuss:

• Basic Java Developer Interview Questions for Freshers
• Java Collections Framework Interview Questions
• Java Advanced Interview Questions—Java Senior Developer Interview Questions
• Java Technical Interview Questions

Basics Java Developer Interview Questions for Freshers

These are junior Java developer interview questions and answers that should be relatively easy for developers of all skill levels to answer during an interview. These common Java interview questions also offer an opportunity to learn more about programming as well. These questions serve as an opportunity to help the developer (and the interviewer) to feel more comfortable, rather than deep diving into the more complex questions related to the framework and advanced design process in Java.

1. What is Java?

Let us start with the basics with this Java interview question. This gets the tone of the interview off to a good start and helps the developer relax before the harder questions come their way. In simplest terms, Java is a programming language. It is centered around objects. It is also highly robust and secure. The developer may also mention that Java is a portable programming language, which means the software that is developed is typically used for more than one computer system.

2. Can You Explain Java Virtual Machine (JVM) in Greater Detail?

This is another softball question. The Java Virtual Machine is a virtual machine that enables computer programs to run Java (and other programs). It operates like a run-time engine. The Java code is compiled by JVM.

3. What is a JIT Compiler?

A just-in-time compiler, or JIT compiler, allows for the execution of computer code in Java. This helps improve the performance of the Java programming language by compiling bytecodes into native machine code at run time. When a method has been compiled, the JVM calls the compiled code of that method directly instead of interpreting it. The developer should also be able to explain what a compile time is as well when answering this Java interview question.

4. Describe the Different Access Specifiers in Java.

This sets the stage for more questions about access specifiers later in the interview. Specifically, the developer should be able to discuss a variety of specifiers. This may include (but may not be limited to) public, private, protected, and default. These keywords define the access scope of methods, classes, and variables.

5. What are the Most Notable Differences Between Java and C++?

This is one of the most basic Java developer interview questions. Each candidate should be able to highlight the differences between each language. Notably, they should highlight how Java is machine and platform-independent, whereas C++ programs solely run on the machines in which they are compiled.

Also, Java internally uses pointers (C++ allows users to use them inside the program). Of course, these are two of many possible differences the developer may highlight with their answer. Other areas they may discuss include (but are not limited to) the design goal for each, what each is used for (i.e., system vs. application programming), the inheritances, the operating overload, and the hardware. There is software available, such as the Java Development Kit by Oracle, that helps developers learn these differences. When asking Java interview questions such as this one, provide them with ample time to answer.

6. What is the Main Method in Java, and Why Is It Static?

The main method is the starting point for Java Virtual Machine (JVM). This is a relatively simple question. However, you can test the developer a little more by asking them more specific questions about Java main method, such as asking them to explain why it is static. The answer: is static to avoid ambiguity.

7. Can You Explain Keywords in Java? What are Some Keyword Examples?

A keyword in Java is a term that has a special function within Java. They also have a set definition in Java. The developer should explain the many uses of the keywords. For instance, they may explain how it can be passed as an argument in the method call or constructor call. The developer should have an overall understanding of these keywords (there are approximately 50 in total). They should also understand their predefined meaning in the compiler and explain it when answering this Java interview question.

9. Can You Highlight the Differences Between a Public Class and a Private Class in Java?

A public class can be accessed from anywhere, whereas a private class can only be accessed inside its own class. Private methods can not be overridden inside Java as they can only be accessed inside its own class. On the other hand, fields, methods, and blocks that are declared inside a public class can be accessed from any class.

10. What are the States in the Life Cycle of a Thread?

There are different states within life cycles. The most notable types of states during the life cycle of a thread are new, runnable, running, waiting/blocked, and dead/terminated. It is important to understand the differences between each state and be able to explain them during the interview.

11. Explain the Super Keyword. Why Would You Use the Super Keyword?

The super keyword is typically used to access the data member of the parent class. However, it can be used in other ways as well. It is integral the developer understands and is able to explain super keywords in Java.

12. What is Class in Object Oriented Programming?

Object-oriented programming (OOP) uses data, classes, and objects to organize software design systems. A class in Java is a user-defined type that declares and defines other types; an object is a single instance of a class. It is important for developers (even those with lesser experience) to have a fair understanding of these relatively simple OOP principles.

13. Describe the Static Method.

Static methods belong to a class. They are not merely instances of a class. A static method has multiple purposes. Notably, They are used when a utility method (or a helper method) does not require an object state. Static methods are a game-changer for many developers as they do not need to create the object to call the static method. They can also access and change the value of a static variable. Ideally, you want to hire a Java developer that understands and implements the static method properly.

Java Collections Framework Interview Questions

The developer should be able to discuss the framework of Java and base classes by answering these interview questions for Java developers. Here are several Java developer interview questions and answers that test the candidate’s knowledge of framework-related topics.

14. Explain the Role of the Heap Memory in Java Development.

The heap memory is a memory component in the Java Virtual Machine. It is created upon the start-up of JVM and can be either static or dynamic. It is primarily used for dynamic memory allocation of Java objects and classes. This is just part of the answer the developer should be able to provide during the interview.

15. Describe the Differences Between Spring Bean and JavaBeans.

Spring beans are objects that are managed by a spring. Spring beans are also instantiated. More broadly, the Spring Framework provides a comprehensive programming and configuration model for modern Java-based enterprise applications. JavaBean is serializable and not managed by the Spring IOC. These are important distinctions. As a follow-up question to this one, consider asking each developer their view about both. Discuss with them the pros and cons of the Spring Framework and the use of Spring beans.

16. What are the Public Static Void Main String Args in Java?

The public static void main in Java is the point from where the program starts its execution. This is one of the most important methods in Java development. The ideal developer has a good understanding of this method and is able to explain it without difficulty when answering this Java interview question.

17. What is the Abstract Class?

An abstract class is (in simplest terms) a class that is declared as abstract. This means it is restricted and cannot be used to create objects. Its method also needs to be implemented. An abstract class can have an abstract method, a non-abstract method, a constructor, and a static method.

18. What is a Finally Clas and a Finally Block?

A final class is also an option, although this is less common. This question more deeply tests the developer’s knowledge of classes and how they are used for program development inside Java. A final block is more advanced and tests the developer’s deep knowledge.

Advanced Java Interview Questions – Java Senior Developer Interview Questions

Below are core Java interview questions for experienced programmers. These Java advanced interview questions, and answers go further in-depth than the questions discussed above. You may choose to use these questions with all developers whom you interview or only for those who have shown a level of experience and knowledge that stands out among the competition.

Java Interview Questions for Developers with 5 Years of Experience

Below are some Java interview questions for freshers. Hiring a less experienced developer may help you meet stricter project budget requirements, but it is essential to ask the right questions to ensure the developer is a good fit.

19. What is the Difference Between an Abstract Class, Child Class, and a Parent Class in Java?

In simplest terms, abstract classes contain abstract methods, which are methods that are declared but do not contain implementation. A parent class, also called a base class or super class, contains child classes (or subclasses). Writing a child class typically involves the use of keywords (see above) and other methods. A child class (or sub-class) is derived from the parent class and may or may not be abstract. The developer should have a detailed understanding of all of the different classes and interfaces and how they are used within Java.

20. Compare the Static Class Method and the Instant Method. What Are the Differences?

The instant method is used for any method that is not declared as static. You do not need to create the object to be called a static method, whereas objects are required with instance methods. This is a relatively simple yet integral distinction that the developer should be able to explain during the Java developer interview.

21. What is the Difference Between Public Void and Static Void?

These indicate how a piece of code can be accessed. A public void serves as the access specifier; it states that the method can be publically accessed. A static void, on the other hand, states that the object is not required to access static members. The developer should be able to describe these basic differences between public void and static void, along with other specifics related to the public (and private) voids and public keywords.

22. What is the Static Variable in Java Used for?

Static variables in Java are used for memory management purposes. They can be applied with variables, blocks, methods, and nested classes. Generally, they refer to the common property of all objects. They receive memory only once at the time of the class loading. The developer should have a detailed understanding of static variables in Java and how they are used. They should also have a more broad understanding of all variable types within Java, including but not limited to local variables, instance variables, and final variables.

23. What Restrictions Are Placed Upon Static Methods?

There are two primary restrictions associated with the static method. For instance, static methods cannot use non-static data members. Additionally, the super cannot be used in a static context (because they are non-static by nature). The developer should understand these restrictions.

24. Is There a Difference Between Nested Class and Inner Class? If so, Please Highlight the Differences.

Nested classes and inner classes are all too often confused and subsequently misused by Java developers. The short answer: Inner classes are non-static nested classes, so there is a difference between the two, and the terms are not used interchangeably. The inner classes are essentially a part of the larger nested class.

25. How Do You Use the Equals Method in Java?

The equals method compares two separate strings and returns them as “true” if they are the same; they are deemed “false” if they are not the same. Most developers use the equals method to compare two strings lexicographically. This is a more advanced question as many freshers do not use the equal method much (if at all) and may not be able to explain it entirely. In other words, this question is a great way to determine the overall experience level and knowledge of the developer.

26. Can You Provide an Example of Multiple Inheritance Use in Java?

With multiple inheritances in Java, a class can inherit from more than one class. In other words, it is a single class that has multiple super classes. The developer should be able to define multiple inheritances and explain how they are used to improve the development process in Java.

Java interview questions for Developers with 10 Years of Experience

Of course, developers who have more than a decade of experience with Java should have a more in-depth understanding, especially if you intend to pay them more than you would otherwise pay a fresher Java developer. Below are Java interview questions for senior developers. These Java interview questions give you more insights into just how good the senior developer is.

27. What is the Role of a Default Constructor in Java?

A default constructor is a method that initializes an object’s state. It is called when an object of a class is created inside Java. There are three types of constructors, which are the default constructor, the parameterized constructor, and the no-arg constructor. The developer should understand the differences between each. Specifically, you can ask them about the default constructor as this is the most basic and essential to understand.

28. Can You Describe String Pool in Java?

String pool in Java is a storage space in Java Heap Memory. It, as the name suggests, stores strings. As a follow-up question, consider asking the developer to describe immutable regarding string. The idea here is to ensure the developer understands what string (and string pool) is inside Java, as it is essential to quality development.

29. Can You Explain the Role of a Copy Constructor in Java?

This is a bit of a trick question as there is no copy constructor in Java. The copy constructor is an integral part of C++. The developer should understand this change with Java and this Java developer interview question helps ensure the developer does not confuse the two. Although there is no copy constructor, the developer is able to copy the values from one object to another, and they should be able to explain the process for doing so.

30. What is a Java Runtime Class in Relation to a Java Runtime Environment?

A Java runtime environment, also called a JRE, loads applications inside of Java for the Java Virtual Machine to execute. The Java runtime class interacts with the Java runtime environment. The developer should understand the relationship between the JRE and each runtime class. As a follow-up Java question, catch blocks and how they are used within run time systems.

31. Please Describe Object Cloning and Both the Advantages and Disadvantages.

This, as the name suggests, refers to the cloning of an object so that you are creating two separate objects that are the same. There are both advantages and potential drawbacks to using the clone () method. For instance, the developer may discuss the ability to avoid writing repetitive code (and subsequently wasting valuable development time) as a key benefit of object cloning. However, there are also drawbacks that the developer should be able to highlight as well. Similarly, you can also ask the developer about pass-by value (and pass-by reference).

32. What is the Relationship Between the Runnable Interface and Threads?

The instances of a runnable interface can run as a thread. The runnable interface is a core interface of Java development, and the developer should have an in-depth of what they are and have the ability to describe them. Also, since Threads are a core component of the runnable interface, they should also be able to explain how they are used. The developer should be able to explain how to implement the runnable interface.

Java Technical Interview Questions

Technical Java interview questions and answers provide a deeper dive into the backend processes. These are the top Java interview questions to test the developer’s knowledge of the technical aspects of Java development. By answering these Java interview questions, you can determine if each developer has the knowledge necessary to complete your project.

33. How Do You Create a Derived Class from a Super Class in Java?

A derived class refers to any class that receives its properties from the super class. The ability to create a derived class is a basic and simple component for both fresher Java developers and senior Java developers. When answering junior Java developer interview questions (and to an extent senior Java developer interview questions) such as this one, they should be able to define both derived class and super class and explain the process for creating a derived class so that it derives its properties from the super class (or base class).

34. How (if at all) are Sleep Method and Wait Method Different and Similar?

The primary difference between the sleep method and wait method is the class upon which they are defined. A sleep method is defined in the Object class; the sleep method is defined in the Thread class. The developer may also discuss lock releasing, which occurs during sleep method but not during wait method.

35. Describe The Purpose of the “This” Keyword in Java.

The this keyword is used regularly with most Java development projects. It is important for the developer to understand the different uses of this keyword. For instance, the developer may discuss how the keyword can be used to implicitly invoke current class methods. However, there are many directions in which the developer can go with this question.

36. Can You Explain the Purpose of the Final Variable in Java?

The final variable restricts the user from making continual updates. It can only be assigned a value once and can only be assigned through the class constructor. The developer should be able to explain the purpose of a final variable in Java development. A good follow-up to this question would be to ask them about what a final keyword in Java is.

37. What are some of the rules for method overloading in Java?

This question tests the developer’s knowledge of method overloading in Java. The overloading method occurs when there is one method with multiple parameters. The developer should be able to explain the rules of method overloading, including whether or not they can be synchronized, how to declare them as static or non-static, and more. As a follow-up, you can ask the developer to explain the differences between method overloading and method overriding.

38. What is the Purpose of Garbage Collection in Java?

The developer should adequately use their space when developing applications inside of Java. This Java developer interview question ensures they are able to do so. A garbage collector, also called garbage collection or GC, in Java is the process inside of Java that allows for automatic memory management.

The purpose of garbage collection in Java is to remove unused objects. This optimizes the storage space inside the Java Virtual Machine. In other words, with this function, the variable has been defined but not initialized. This method is also known as the gc () method inside Java. For a follow-up question, consider asking the developer how garbage collection is controlled (see below).

39. How is Garbage Collection Controlled?

Garbage collection is managed through the Java Virtual Machine. Most project developments contain some level of garbage collection. The ability to control this throughout each project is essential. The ideal developer has experience controlling garbage collection inside of the JVM.

Conclusion

We hope these Java programming interview questions have helped. Do you intend to interview and hire a Java developer? JayDevs can provide you with proven and reputable Java developers. To learn more and get started, contact us today.