69 Java Senior Developer Interview Questions (Some could Break your Neck)

If you're looking to become a senior developer, then it's important that you know what questions will be asked of you. In this blog post we'll look at Java interview questions and answers for senior developers.
by Billy Stone » Remote Work Nerd » 
last updated on November 13th
These are the most often asked Java interview questions for those with five or more years of experience as a core Java programmer or developer. If you want to become a senior developer, make sure your resume reflects these traits when an interviewer says "walk me through your resume."
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Java is a popular programming language that many companies use for their web applications. As a result, there are plenty of Java developer jobs available in the market today. If you want to get one of these great jobs, you will have to go through an interview! But how can you prepare yourself? We have gathered 25 most asked java senior developer interview questions and answers so that you know what to expect when going into your next interview.

java senior developer thinking about answers for his job interview

69 java senior developer interview questions with examples answers

In order not to sound like an amateur during your interview, it is important that you have the proper knowledge about the company and what they do.

This ensures a smooth-sailing experience from beginning until the end. These questions & answers make sure you don't give off any red flags:

Q1: What is JVM?

Answer: JVM stands for Java Virtual Machine. Java is a programming language designed to be platform agnostic. It uses bytecode, which can be executed by any JVM and take advantage of the specific instructions in hardware platforms without requiring recompilation or re-writing for each different type of system where it might run - this makes Java virtual machines possible!

Q2: What is the difference between JDK and JRE?

Answer: The Java Runtime Environment (JRE) is the software needed to run a Java app, contains necessary parts of the Java platform including one or more implementations of the standard class libraries, and implementation of the Java virtual machine (VM), and other components.

Q3: What does JSR stand for?

Answer: A Java Specification Request (JSR) is an expression of desire for new or important changes in the existing specification, which will be submitted at Oracle’s JCP. Once approved by consensus among members from all over this process defines and develops extensions to future standards within the programming language Java as well as alterations to its runtime environment where communities work together on these tasks.

Q4: What is Application Context?

Answer: The Java Context is used to obtain information about the application environment. It holds various system properties, input parameters, and other general data required during the execution of an application. Both load bean definitions and wire them together just like any other factory would do - but what makes them so special? Application contexts dispense their components upon request!

Q5: What is JDBC?

Answer: The Java Database Connectivity (JDBC) is a standard application programming interface for the programming language Java that defines how a client may access specific data-source. It enables you to connect to database servers and execute SQL statements, which are encapsulated in either Data Definition Language(DDL) or Data Manipulation Language(DML). This provider allows users to choose between databases and enables developers to write database applications in Java without the need for them to understand how a specific database works.

Q6: What is reflection and why is it useful?

Answer: Reflection is the ability of a computer program to examine, introspect, and modify its structure and behavior at runtime. By using this technique you can create applications that can perform operations on an object's data member or call one of its methods without knowing any information about it until run time. This also enables developers to implement some Security Manager protection.

Q7: What is a thread? Why are they useful? How can you create one in Java?

Answer: A Thread is an independent, concurrent path of execution within the same process as it enables multithreaded programming by splitting up tasks into different threads and executes them concurrently. In general, this increases performance because multiple threads can read, modify and write to memory at the same time. A thread is a single sequential flow of control within a process - this enables programs to perform multiple tasks simultaneously.

Q8: What are some common data structures?

Answer: There are many different kinds of Data Structures available in Java applications such as Lists, Stacks, Queues, and Maps. They are similar to arrays in that they store data - but also different because instead of using integer indexes for accesses elements by their position at the time of insertion or retrieval they allow you to specify a key that can be used as an identifier when accessing items within them.

Q9: What is the difference between a class and an object?

Answer: A Class is the blueprint for creating objects, it defines all of their properties including methods that can be used to perform tasks. An Object on the other hand is one instance of that particular type or class - this means that each time you create a new object within your code it will have its own set of values and properties.

Q12: What is the function of the Continuous Integration (CI) server?

Answer: A CI server is a computer program that automatically builds and tests software projects hosted on another computer system. It typically performs both continuous integration - which often includes running automated unit tests, static code analysis rules upon check-in to determine whether the new changes work properly with all existing features of the application - as well as nightly builds for every successful check-in.

Q13: What does it mean for a method to be thread-safe?

Answer: A method is called Thread-safe if the results of executing that particular function are guaranteed not to be affected by other threads accessing its shared data at the same time. This means you should never have more than one copy of the program running - which will prevent it from being executed as expected.

Q14: Name three of the most commonly used Java collections?

Answer: The Collections Library defines several implementations that can be used to store and retrieve data efficiently in a specific way, some examples are HashSet, TreeSet, Stack, and ArrayList. These containers have been designed so they can be accessed by multiple threads concurrently without compromising the integrity of their data.

Q15: What is multi-threading? Why would you use it?

Answer: Multi-Threading allows the software to perform more than one task at a time or execute different parts of its code simultaneously - this speeds up your application's performance and responsiveness when users are interacting with it.

So, let's take a short break, and continue with tons of great senior java developer interview questions:

Q16: Can == be used on enum?

Answer: Yes. The language specification provides a guarantee that enums will behave in predictable ways. For instance, you can use == to compare instances of an enum type with one another and the result is always true or false based on how it was declared at compile time!

Q17: What is an Iterator? Why would you use it?

Answer: An iterator implements java interfaces from the java collections library - this provides several benefits that can be useful in your applications such as removing and inserting elements within a collection, traversing the list of items based on the criteria you define without knowing its underlying structure or how it is implemented.

Q18: Which Operator do we use to implement logical AND?

Answer: A && (double ampersand) operator is used to implement logical AND. A conditional statement with a series of boolean expressions will only return true if all the Boolean conditions are met, so this means that both operands must be valid and it can’t just depend on one or two - this implementation provides more secure and reliable code than using || (double pipe) or | (single pipe).

Q19: What is the difference between a break statement and a continue statement?

Answer: A break statement will terminate one of two loops - either a switch-case block, which implements multiple cases for selection. When it encounters this junction in code during execution it will immediately jump out to execute the next line of code after the closing brace.

A continue statement is used to implement a loop-continuation condition at runtime - this means it will check each iteration case before executing its statements and if the test fails, which is indicated by evaluating false for an expression that returns Boolean data type, then control will be transferred directly to the start of the loop to begin checking the condition again.

Q20: What is a final variable? Why would you use it?

Answer: A final local or static variable can only be assigned once - this means that when an attempt is made to assign another value during program execution then it will produce either a compilation exception, which are used by the compiler to inform you of an error before it occurs at runtime, or it will produce a warning. These are useful because they can prevent data corruption and memory leaks which cause serious problems if left unfixed in your code!

Q21: Compare the sleep() and wait() methods in Java?

Answer: The sleep() method is used to implement a delay during program execution - it will suspend the current thread for an amount of time, which can be specified using milliseconds. This means that other threads can execute while you wait and this implementation does not have any parameters or return values.

The wait() method on the other hand is used for synchronizing and waiting on other threads to finish executing before continuing - this means that it will release the current object’s monitor and allow another thread of execution to access its code. When a notify() or notifyAll() method is called by any of these threads then the wait() method will return, so you can be assured your code won’t be stuck waiting if another thread calls it to end its execution.

Q22: What is the difference between stack and heap?

Answer: The stack refers to memory that has been allocated specifically for a certain purpose, which means you can access this data quickly because it doesn’t require any indirection - when control is transferred to this memory, the program counter will increment by an amount equal to its size and when control is returned it does so in reverse order.

The heap on the other hand refers to memory that has been allocated for a certain purpose outside of your code - you can allocate and deallocate data from this section at runtime but because there is no fixed size to the amount of memory allocated, then you must implement your algorithms for managing it.

Q23: What is an abstract class? How does it differ from other classes?

Answer: An abstract class can’t be instantiated because they contain at least one method or field that has been declared as either private or final, which means it can’t be overridden in subclasses. An abstract class is used to define common methods for derived classes, so they don’t have to implement their version of these functions - this allows you to manage the code that gets executed when invoking one of these actions at runtime by using polymorphism!

Q24: What is an interface?

Answer: An interface, like abstract classes, can’t be instantiated and defines a contract that all of its derived types must implement - this means they will declare their methods but don’t provide any implementations. Interfaces are useful because you can enforce specific behavior for these functions when implemented in the classes that derive from them, which allows you to avoid having multiple functions with the same name but different behaviors.

Q25: What is a local variable? Describe its scope and lifetime?

Answer: A local variable can only be used within the method where it’s defined - this means that when control leaves the block of code then any data stored by this variable will be destroyed. The scope of a local variable is the section within your program where you can access it, which means if there are any nested blocks or loops then you must ensure that they’re using different variables to avoid collisions!

If you made it this far then congratulations! You’ve should now have a strong grasp of java interview questions for senior developers. On to the next questions. Ready? Let's go!

Q26: What do you understand by checked and unchecked exceptions?

Answer: Checked exceptions occur when your code encounters a situation that is out of the ordinary and needs to be handled, which means they inherit from the Exception class. Unchecked exceptions, on the other hand, indicate that some kind of problem has occurred but it’s not an error - these are subclasses of RuntimeException so there isn’t any need to handle them.

Q27: Does Spring Bean provide thread-safety?

Answer: Spring beans are thread-safe because they follow the singleton pattern, which means only one instance of its class will be created and this is shared between all threads that require it.

Q28: What do you understand by a service layer in an enterprise application?

Answer: The service layer provides access to services or functions required by your program - these are usually implemented as Enterprise Java Beans, which are objects that encapsulate business logic and can be used by clients without knowing how they work.

Q29: What is the difference between a constructor and a method?

Answer: A constructor is called when an object of its class is instantiated - it’s declared like any other method but has the same name as its class and doesn’t have a return type. A method, on the other hand, is used to perform actions when called from within your program - it can either be a static or non-static function that may or may not accept parameters.

Q30: What do you understand by an API? How does it differ from an SPI?

Answer: An application programming interface (API) is a set of classes, methods, and functions that provide the building blocks for your program - you should use these whenever possible because they’re well-tested by other developers to ensure compatibility. Service provider interfaces (SPI), on the other hand, are implementations of an API that allow you to define what will be provided in your code.

Q31: What is the difference between a JTable and a TableModel?

Answer: A JTable provides access to data stored in your program, which allows users to search, sort, edit it, etc., by using their mouse or keyboard input - this means you need to provide your TableModel. A TableModel, on the other hand, is responsible for providing access and editing functionality by using its methods and listeners - it also provides information about rows in a JTable so that they appear as expected.

Q32: What are the differences between an inner class and an anonymous class?

Answer: An inner class is defined as a member of another class and has access to all its members - it can be instantiated independently but only if an instance of the outer class exists. A local or anonymous class, on the other hand, does not have any name associated with it so you do need an instance of the enclosing object before creating them.

Q33: What is the difference between an Iterable and an Enumeration?

Answer: An iterator in Java is used to step over a container, which means there’s no need for external iteration - this makes them faster than enumerations when you’re using multiple loops. Enumerations are objects that allow you to loop through a container, which means you can use them with other loops as well.

Q34: What do you understand by the term referential integrity?

Answer: Referential integrity is when data in two related tables correspond to each other - if this isn’t true then referential actions may cause problems when an application tries to update the data.

Q35: How can you implement a cache in Java?

Answer: A cache, which is also known as buffer, stores frequently accessed data and information so it doesn’t have to be read from or written back to its source each time - this will reduce overhead by decreasing latency and increasing throughput.

Q36: What is a framework?

Answer: A software framework provides the building blocks for your program as well as their implementation so you can avoid having to write everything from scratch - this allows developers to focus on other parts of the application and have less code to worry about.

Q37: Is Java pass-by-reference or pass-by-value?

Answer: Java is pass-by-value, which means a copy of the original object will be made when passing it into a method or constructor. This also means that modifying one variable won’t change another unless they have been assigned to point at the same object in memory - this makes them safer because if an application crashes then only one

Q38: Is there a static class in Java?

Answer: No, a static class can’t be instantiated and only has static methods - this means you don’t have to worry about creating an instance of the class before using it.

Although this is one of the core java interview questions for senior developers, which comes up almost every time!

Q39: What do you understand by Java annotations?

Answer: Annotations are used to add metadata or descriptive tags in your code for other programs to read - these include the compiler and development tools like debuggers.

Q40: What is a local variable?

Answer: A local variable in Java is used inside of blocks or method bodies, which means they can only be accessed from within them - this helps keep memory usage low because it doesn’t occupy memory outside of where it is used.

Q41: What do you need to implement when extending the class Thread?

Answer: When creating an instance of a thread, every object needs access to its context (which includes information like environment variables and socket connections) or at least be able to pass their implementation onto others for them to use - this is why you need to implement the Runnable interface.

Q42: How can you generate a random number in Java?

Answer: To create a random number that is between two values, use the method nextInt() from java.lang.Math class - it’s also possible to have this function return floating-point numbers as well.

Q43: State the features of an interface.

Answer: Interfaces are templates that contain only the signature of methods. The method's signature consists of numbers, types (values/references), and ordering for each parameter it contains; there is no implementation on its own because interfaces define only how something works without describing what they do in practice - this can be done by instantiating an interface with one or more implementations defined within function bodies however these definitions must also conform to their declared "interface" specification which does not allow any member variables themselves.

Q44: What do you understand by cryptography?

Answer: Cryptography is used to secure data and communications, which includes encoding messages so they cannot be read by anyone else - this is used in many different applications like SSL/TLS for websites and SSH for remote servers.

Q45: What are the differences between continuous integration, continuous delivery, and continuous deployment?

Answer: Continuous integration is used to build and test applications automatically every time there are changes, which means it’s frequently done by developers as they write code. Continuous delivery builds on this so that these new features can be deployed into production without human intervention. Continuous deployment does both of these as well as automatically notifying other people in the organization about their results and what was done.

Q46: What is an immutable class?

Answer: An immutable object cannot be modified after it has been created, which means that the only way to change them is by creating a new instance with different values - this makes them very useful for building cache objects or settings files because their value can’t be changed by another thread or process.

Q47: What is an abstract class?

Answer: An abstract class can’t be instantiated and instead acts as a template for other classes to extend - this makes it possible to define functions once and have them automatically used by all child objects so they don't need to be re-written every time.

Q48: What is JAR?

Answer: Java Archive files are used to bundle multiple public classes into a single file with the .jar extension - this allows developers and companies to distribute their software in an organized way that makes it easy for others to import them.

Q49: List some of the security implications when working on a web application.

Answer: Websites that handle a lot of user information need to securely store this data in a way that protects it from people trying to access them illegally. This is achieved by encrypting sensitive fields and storing passwords as hashes instead of plain text, which means they cannot be used directly because the encryption algorithm protecting them needs the original text to create the encrypted version.

Q50: What are some of the security implications when working on an Android application?

Answer: An app needs permissions before it can access sensitive data, which is usually given by users after they install them so that only apps with necessary information can use it - if a user denies these permissions or deletes their app, it cannot access this information anymore.

Q51: How can you improve the security of a web application?

Answer: One way to protect an application is by using secure sessions where all user data and operations are done on separate subdomains so that people trying to steal them won't be able to use or see them - this is done by using a cookie with the secure flag set.

Q52: How can you improve the security of an Android application?

Answer: One way to increase mobile app security is by reducing permissions it needs - this allows people to install them more easily because they don’t have as many decisions about what data and abilities are given to them.

Q53: What is Controller in Spring MVC framework?

Answer: Controllers provide a way for you to define application behavior through an interface. They interpret user input and transform it into models that users see when using the view you defined, which is implemented in Spring as abstract controller classes with many possibilities depending on your needs!

Q54: What is DAO?

Answer: The Data Access Object represents an application data source used by other parts of the application to make queries and perform other functions - this makes it possible for you to separate data-related code from your controller by using interfaces that are injected into repositories.

Q55: What is a Factory Bean in Spring?

Answer: A bean whose responsibility is creating new beans on request, which means they can encapsulate their own set of dependencies and make them available to objects defined elsewhere in your Spring application.

Q56: What is a Service Bean?

Answer: A bean whose responsibility is performing actions on other beans by using the information they provide, which means that you can use services provided through dependency injection without worrying about how they are implemented or where their data comes from!

Q57: What is a Repository?

Answer: The responsibility of repositories in Spring MVC applications is to store and retrieve information from their data sources, which means they are the interface that your controller uses to access application functionality. They can be used by other objects as well depending on what you need!

Q58: How do you organize beans in a Spring application?

Answer: The concept of dependency injection allows you to use classes and their dependencies with no need for hard coding because they are shared through the container - this means that their relationships can be declared by using qualifiers on your parameters so that specific implementations can be injected based on what is available.

Q59: What benefits do you get from using a Repository pattern in your Spring application?

Answer: You can use repositories to encapsulate business logic or data access code used by other objects to make it reusable and testable, which means that the responsibilities of controllers are reduced because they don't need to handle these concerns on their own. This allows for easier maintenance over time because you can change how data is accessed without affecting the rest of your application!

Q60: How do you integrate Spring Security into an existing web application?

Answer: The first step in integrating security into a new or existing application with Spring is including dependencies, which means that for this example I used spring-boot-starter-security and spring-boot-starter to include all the dependencies I needed.

Q61: How do you secure controllers in Spring MVC applications?

Answer: To secure your controller, you must decorate it with @PreAuthorize to require user authentication or authorization based on whatever security configuration is available at the time - this means that if a user isn't authorized due to insufficient permissions, they are automatically redirected elsewhere.

Q62: How do you secure routes in Spring MVC applications?

Answer: The main way that you can define route security is by using the @PreAuthorize annotation on methods of your controller - this means that if a user isn't authorized due to insufficient permissions, they are automatically redirected elsewhere.

Q63: What does the WebSecurityConfigurerAdapter do?

Answer: The main thing that this class is responsible for in Spring MVC applications is configuring supported authentication mechanisms, which means it allows you to configure what type of security set up your application will use like form-based authentication or basic authentication. It also allows you to configure what type of security configuration is allowed for your application.

Q64: What does the @PreAuthorize annotation do?

Answer: The main thing that this annotation allows you to define in Spring MVC applications is whether or not a user must be authenticated before being able to call a controller, which means it checks if a user is authenticated before allowing them to access a controller.

Q65: What is the difference between fail-fast and fail-safe?

Answer: Fail-fast is the default behavior in Spring that causes an exception to be raised as soon as a single failure occurs, which means it's useful for debugging but protects against unexpected failures. Fail-safe will allow multiple exceptions to occur before throwing one thus allowing you some time to catch them all - this might happen if your application depends on things happening in a specific order.

Q66: What does @PreDestroy do?

Answer: The main thing that this annotation allows you to define in Spring MVC applications is whether or not it gets invoked when the request ends, which means if any cleanups need to be done like closing connections or releasing memory, they will get called before the request ends.

Q67: How can you check if a user has been authenticated in Spring MVC?

Answer: You can use the HttpServletRequest to find out if they have been authenticated by checking their authentication type, which means that this will return null for unauthenticated users but it will be able to tell from there if they are authenticated.

Q68: What is the JIT?

Answer: The Just-in-time compiler (JIT) is a Java Virtual Machine that compiles bytecode into machine code at runtime, which means it takes place when your program starts running and isn't required for the entire process.

Q69: What is a Spring IoC container?

Answer: The IoC container is responsible for how objects are created and managed in Spring, which means it allows you to configure dependencies so that they can automatically be injected into your classes when needed.

Conclusion

Those core java interview questions for experienced developers are a great place to start if you're looking for some pointers on what interviewers may ask when it's time to take the next step in your career.

You'll find that these questions have been categorized by difficulty level, so you can go through them at your own pace and work up from easier topics like basic syntax to more complex concepts like error handling. We hope this article has helped prepare you for success!