20 Java Developer Interview Questions & Answers
Below is a list of our Java Developer interview questions. Click on any interview question to view our answer advice and answer examples. You may view 5 answer examples before our paywall loads. Afterwards, you'll be asked to upgrade to view the rest of our answers.
1. Tell me about the Java Reflection API?
How to Answer
As the interview progresses, the technical questions will become more difficult. This indicates that the interviewer is gaining confidence in your qualifications and is willing to explore your background in more depth. Continue to answer the questions, in the same manner, keeping your answers brief and to the point.
Written by William Swansen on December 21st, 2020
Answer Example
"The Java Reflection API enables you to test and modify applications while they are running. You can inspect the various elements of the java programming language, seeing the details. Java developers use this to debug and improve their programming."
Written by William Swansen on December 21st, 2020
2. What are some examples of JDBC drivers?
How to Answer
This is a follow-up to a previous question. Any time you provide an interviewer with the answer, you should anticipate a follow-up question. This indicates that they either need more information or have a specific interest in this topic. If there are several follow-up questions about the same topic, they indicate that the subject is important to their operations. You should use it as a clue to talk more about the subject when answering their questions. Your answer to this question may sound something like this: "There are four basic types of JDBC drivers. The drivers work in conjunction with the JDBC API to connect with and extract information from databases. The four drivers are ODBC, Native API, Pure Java driver for Database Middleware, and Direct-to-Database Pure Java Driver."
Written by William Swansen on December 21st, 2020
Answer Example
"There are four basic types of JDBC drivers. The drivers work in conjunction with the JDBC API to connect with and extract information from databases. The four drivers are ODBC, Native API, Pure Java driver for Database Middleware, and Direct-to-Database Pure Java Driver."
Written by William Swansen on December 21st, 2020
3. Please describe the JDBC API and discuss how it is used?
How to Answer
Another classic technical question asking you to define a concept and then describe how it is used. Continue to keep your answers brief and to the point, and feel free to provide an example if you think it will embellish or enhance your answer. Always be prepared for follow-up questions.
Written by William Swansen on December 21st, 2020
Answer Example
"JDBC stands for Java Database Connectivity. The API enables java programs to work with relational databases. This enables the program to connect with the database, run SQL queries, and process the results."
Written by William Swansen on December 21st, 2020
4. When programming in Java, can you have an empty catch block?
How to Answer
This is an example of an operational question. Operational questions evaluate specific elements used in your job. Like technical questions, answers to operational questions should be brief and to the point. You should also anticipate follow-up questions if the interviewer needs additional information or wants to explore the topic in more detail. Your answer to this question can sound something like this: "While you can use an empty catch block while programming in Java, it is not advised. The problem this creates involves debugging the program if the empty catch block were to catch an exception. There will not be any information about the exception. Finding the issue with no information in the log could be very time-consuming."
Written by William Swansen on December 21st, 2020
Answer Example
"While you can use an empty catch block while programming in Java, it is not advised. The problem this creates involves debugging the program if the empty catch block were to catch an exception. There will not be any information about the exception. Finding the issue with no information in the log could be very time-consuming."
Written by William Swansen on December 21st, 2020
5. How does an OutOfMemoryError impact a program written in Java, and how can this be corrected?
How to Answer
This is an example of a hybrid technical and operational question. While technical questions ask you about specific concepts, operational questions explore how you do your job. This question first asks you to define how a specific concept impacts your program and then discuss how to remediate it. As with technical questions, hybrid or operational questions should be answered briefly and to the point.
Written by William Swansen on December 21st, 2020
Answer Example
"An OutOfMemoryError is created by the JVM when there is no memory available for it to use. This will result in a program halting. The simple way to fix this is to allocate more memory to run in the java application."
Written by William Swansen on December 21st, 2020
6. Please define a CountDownLatch in the context of Java?
How to Answer
You'll note that this question simply asks for a definition of a term used within the java programming language. You can only provide the definition or enhance your answer by describing how it is used and providing an example. Your choice of how to respond to this question will be based on your perception of the interviewer, the interview's progress, and whether you feel providing a more in-depth answer will better demonstrate your qualifications for the job.
Written by William Swansen on December 21st, 2020
Answer Example
"The CountDownLatch, as used in Java is a synchronizer which enables a thread to wait for one or more other threads before it starts processing."
Written by William Swansen on December 21st, 2020
7. Talk about what a Java timer class is and how you schedule a task to run after a specific interval?
How to Answer
Another classically formatted technical question. You are being asked to define a concept and then discuss how it is used in your work. Remember to keep your answer brief and to the point, and provide an example if you think it will enhance your response. Always be prepared for follow-up questions when you provide an answer.
Written by William Swansen on December 21st, 2020
Answer Example
"A Java timer class is a subclass of a java.util package. It is used to schedule a thread that is executed in the future. An example of one use is for scheduling a task which will be run at regular intervals."
Written by William Swansen on December 21st, 2020
8. Can you discuss the differences between a user and a daemon thread?
How to Answer
A common format of technical questions is asking you to compare two terms. The best way to respond to these types of questions is to first define the terms, and then compare the differences or similarities. You may even want to provide an example to help illustrate your answer.
Written by William Swansen on December 21st, 2020
Answer Example
"The differences between a user thread and a daemon thread are how they are created, and their impact on JVM. User threads are created by programmers, while daemon threads run in the background. If a user thread is present, the JVM will not shut down, and the program will continue to run. However, the presence of a daemon thread does not prevent the JVM from terminating."
Written by William Swansen on December 21st, 2020
9. Can you tell me what a Compare and Swap algorithm is and how you use it when coding in Java?
How to Answer
This is a more complex technical question, which asks you to define a term and then discuss how it is used when creating a Java program. Regardless of whether a question is simple or complex, it would be best to keep your answer brief and to the point. The interviewer will either ask for more information or move on to the next topic.
Written by William Swansen on December 21st, 2020
Answer Example
"Compare and Swap is a type of instruction which helps to synchronize threads in a multi-threading environment. The way it works is to examine the content of a memory location and, if it matches another location, it modifies the value of the content and creates a new value. This prevents the content from being used by another thread and a write operation failing."
Written by William Swansen on December 21st, 2020
10. What is a marker interface, and how do you use it when writing Java code?
How to Answer
The fact that this is a technical question is obvious since it asks you to define a term and then discuss how it is used. Make sure you answer each part of the question in the order asked. This will help the interviewer follow your answer and confirm that you are listening to their questions during the interview.
Written by William Swansen on December 21st, 2020
Answer Example
"A marker interface, as it is used in Java, is a design pattern which provides runtime information about the objects within the program. It also enables the addition of metadata with a class even though the Java language doesn't implicitly support metadata. When coding in Java, the marker interface is used as an interface which doesn't specify a method."
Written by William Swansen on December 21st, 2020
11. What are the key elements of the Java programming language?
How to Answer
This is the type of question an interviewer will use to begin the conversation, learn more about your background, and collect information they can use throughout the interview. This question also provides you the opportunity to direct the interview towards a subject area that you are familiar with and comfortable responding to questions about. Throughout the interview, keep your answers brief and to the point. This will encourage the interviewer to ask follow-up questions about the same topic or move on to a new subject.
Written by William Swansen on December 21st, 2020
Answer Example
"There are several key features of the Java programming language. First, it is simple to learn. Next, Java is somewhat object-oriented and enables programmers to manage their code using objects. Several other key features of Java include its portability, platform independence, security, and the large library of code available to programmers."
Written by William Swansen on December 21st, 2020
12. What is Composition, as used in Java?
How to Answer
As the interview progresses, the hiring manager will continue to ask you technical questions about writing programs within Java. Some of these will be very simple, asking you to define basic concepts that any programmer should know. Others will be more complex and require you to give longer, more complicated answers to define the concept, describe how it is used, and give an example of how to write the code. The best way to prepare for these is the practice these types of questions, stating the answers out loud, so you become comfortable doing this.
Written by William Swansen on December 21st, 2020
Answer Example
"Composition is a method used in Java to implement has-a relationships within classes. This facilitates code reuse through object composition. When using composition, you implement instance variables that refer to different objects. The benefit is to provide visibility of the objects to other classes so they can reuse them."
Written by William Swansen on December 21st, 2020
13. How are access modifiers in used Java?
How to Answer
Technical questions asked in this fashion are requesting that you describe how a concept or process is used when programming in Java. When answering this type of question, you may want a skip defining the concept and simply state how it is used. You can still provide an example if this helps clarify your answer. Make sure to keep your answer brief and to the point. The interviewer will ask a follow-up question if they need additional information.
Written by William Swansen on December 21st, 2020
Answer Example
"Access modifiers are used to establish accessibility to classes, methods, and other members when writing code in the Java programming language. The four types of access modifiers are default, public, private, and protected. These define how the classes, methods and members can be accessed."
Written by William Swansen on December 21st, 2020
14. Can you discuss what a static import is and what the pitfalls of using this are?
How to Answer
This technical question asks you to first define the concept and then describe some features of its use. This is a common format for technical questions. When answering a question during an interview, you should anticipate follow-up questions. These indicate that the interviewer needs additional information or has a strong interest in the topic they are asking about. It may also be an indicator that the topic is important to the operations of the organization.
Written by William Swansen on December 21st, 2020
Answer Example
"Static import is the process of importing the class and the method variable with the class name from another class. This makes the class available. The pitfall of using this methodology is that it may cause confusion if it is overused and thereby trigger the program to malfunction."
Written by William Swansen on December 21st, 2020
15. How is a volatile keyword used in Java?
How to Answer
This technical question assumes you know the definition of the term the interviewer is asking about and only requests that you describe how it is used. By carefully listening to the interview's questions, you will provide the answer they are expecting. If you begin to think about your answer while the interviewer is still talking, you may miss the question's essence and give an answer which is not related to the question.
Written by William Swansen on December 21st, 2020
Answer Example
"A volatile keyword is used in Java with variable and threads which read its value directly from its memory location. This ensures the value is read exactly as it is contained in the memory location, and that the threads or variables do not cache it in case it changes."
Written by William Swansen on December 21st, 2020
16. Can you define the final keyword in Java?
How to Answer
This technical question asks you to define a concept within Java. When interviewing, you should carefully listen to the questions you are being asked. Do not start to formulate your answer until the interviewer has completed asking the question. This will ensure that you understand what they are asking and that your answer corresponds to what they are looking for. When answering this question, the mistake you can make is providing too much information since you are only being asked to define the concept.
Written by William Swansen on December 21st, 2020
Answer Example
"Within Java, the final keyword is used with the class to make sure that no other class can extend it."
Written by William Swansen on December 21st, 2020
17. In your opinion, Is Java Pass By Value or Pass By Reference?
How to Answer
You may note that this question asks you for your opinion, even though it is technical. Not all technical questions have finite answers. Some may be relevant to the work you do or the type of experience you have writing programs. It is okay to state an opinion about a topic as long as you can support your answer. When asked a question of this type, you can anticipate follow-up questions asking why you believe this to be the right answer.
Written by William Swansen on December 21st, 2020
Answer Example
"This is an interesting question. If you ask a group of Java developers, some will say that Java is pass by value, while the others will say pass by reference. In my opinion, Java is pass by value. This is how it is defined in the Java Spec. Java method parameters directly associate variable passing and method calling. The exception is when we pass a reference of complex types defined as method parameters, the memory address is copied to a new reference variable."
Written by William Swansen on December 21st, 2020
18. How is Enum used in Java?
How to Answer
You should already recognize this as a technical question. It is asking you how a concept or process is used within the Java programming language. Continue to answer technical questions directly and briefly, with little embellishment, anticipating follow-up questions from the interviewer.
Written by William Swansen on December 21st, 2020
Answer Example
"Enum is a type whose field is made up of fixed sets of constants. An example of this would be the setting of times within a Java program as morning, noon, afternoon, and evening. These become key words used to create enum types, which are similar to a class."
Written by William Swansen on December 21st, 2020
19. Can you discuss the importance of the main() method in Java?
How to Answer
This is another example of a technical question. As a Java developer, you can anticipate that most of the questions you will be asked during an interview will be technical. The best way to prepare for these is to review the concepts used in Java programming and understand the processes, libraries, tools, and methodologies Java developers use. Being familiar with these will help you prepare for the questions you are likely to be asked.
Written by William Swansen on December 21st, 2020
Answer Example
"The main() method as it is used in Java provides programmers with an entry point for any code they are writing. It defines the syntax to run a program within the Java language. It also enables Java to access the code without initializing a class. The value contained within the parentheses is an array of string related to runtime arguments."
Written by William Swansen on December 21st, 2020
20. Within Java, what are the differences between path and classpath variables?
How to Answer
This is a common format of a technical question. Technical questions ask you about concepts or items related to the work you do. They sometimes ask you to compare similar concepts or to describe how they are used. When answering technical questions using this format, you should first define the terms you were asked about. You then either compare them or describe how they are used. You may provide an example if it helps illustrate your answer.
Written by William Swansen on December 21st, 2020
Answer Example
"Both path and classpath are environmental variables which the operating system uses to locate executables. The OS locates the executables in a directory location, which is defined by these variables. The difference between a path and classpath variable is that a classpath is very specific to Java and can be defined as a directory, ZIP file, JAR file or another type of variable."
Written by William Swansen on December 21st, 2020