400+ Senior Java Developer Interview Questions and Answers

Remove the Kth node from the end of a singly linked list.

• Traverse the linked list to find the length 'N'.

• Calculate the position to delete from the beginning as 'N - K + 1'.

• Delete the node at the calculated position.

• Handle edge cases like deleting the head or tail node.

Find the node where two linked lists merge

• Traverse both lists to find their lengths and the difference in lengths

• Move the pointer of the longer list by the difference in lengths

• Traverse both lists simultaneously until they meet at the merging node

Merge two sorted linked lists into a single sorted linked list with linear time complexity and constant space usage.

• Create a dummy node to start the merged list

• Compare the values of the two linked lists and add the smaller value to the merged list

• Move the pointer of the merged list and the pointer of the smaller value list forward

• Continue this process until one of the lists is fully traversed

• Append the remaining elements of the other list to the merged list

• Return the head of ...read more

Design a Least Recently Used (LRU) cache data structure that supports get and put operations with capacity constraint.

• Implement a doubly linked list to keep track of the order of keys based on their recent usage.

• Use a hashmap to store key-value pairs for quick access and update.

• When capacity is reached, evict the least recently used item before inserting a new item.

Java is platform-independent because the code is compiled into bytecode which can run on any platform with a JVM, making the JVM platform-dependent.

• Java code is compiled into bytecode, which is a platform-independent intermediate code

• The JVM interprets and executes the bytecode on different platforms

• The JVM acts as a layer of abstraction between the Java code and the underlying platform

• The JVM is platform-dependent because it needs to be implemented specifically for each plat...read more

The life cycle of a thread in Java involves creation, running, waiting, and termination.

• A thread is created using the 'new' keyword or by implementing the Runnable interface.

• The thread starts running when the start() method is called.

• During execution, a thread can enter a waiting state using methods like sleep() or wait().

• A thread terminates when its run() method completes or when the stop() method is called.

Abstract classes are used for code reuse and interfaces are used for multiple inheritance and loose coupling.

• Abstract classes can have both abstract and non-abstract methods while interfaces can only have abstract methods.

• Abstract classes can have constructors while interfaces cannot.

• Interfaces are used when a class needs to implement multiple behaviors while abstract classes are used for code reuse.

• Interfaces promote loose coupling while abstract classes promote tight coupli...read more

Designing a concurrency model for a high calling java application to ensure thread safety and maximize throughput while minimizing deadlock risks.

• Use a combination of thread pools and executor services to manage concurrent requests efficiently.

• Implement synchronization mechanisms such as locks, semaphores, or atomic variables to ensure thread safety.

• Utilize non-blocking algorithms and data structures to reduce contention and avoid deadlocks.

• Consider using asynchronous program...read more

This response covers key Java concepts including runtime polymorphism, method overloading, array manipulation, and threading.

• 1. Runtime polymorphism occurs when a method call is resolved at runtime. Example: Method overriding in subclasses.

• 2. In 'Developer d = new Employee();', if d.work() is called, the 'work' method in Employee class will execute if overridden.

• 3. Yes, static methods can be overloaded by changing the parameter list. Example: 'static void method(int a) {}' an...read more

I would assess the legacy system's data exchange formats and communication protocols, then design a seamless integration plan.

• Analyze the data exchange formats used by the legacy system and determine compatibility with Java application

• Identify the communication protocols utilized by the legacy system and ensure they can be integrated with Java

• Design a middleware layer or API to facilitate communication between the legacy system and Java application

• Implement data mapping and t...read more

Implement secure authentication and authorization using Auth or JWT token to prevent security vulnerabilities.

• Use HTTPS to encrypt communication between client and server to prevent eavesdropping.

• Implement strong password policies and use password hashing to securely store user credentials.

• Use JWT tokens with short expiration times and refresh tokens to prevent token theft.

• Implement role-based access control to ensure users only have access to authorized resources.

• Regularly u...read more

Setting port number as 0 in Spring Boot for a service

• Setting port number as 0 allows the operating system to choose an available port

• This is useful when running multiple instances of the same service on the same machine

• To set port number as 0 in Spring Boot, add 'server.port=0' to application.properties or application.yml

Optimize microservice performance with caching strategies like Spring Cache and distributed caching solutions.

• Implement Spring Cache Abstraction to cache method results, reducing database calls.

• Use annotations like @Cacheable, @CachePut, and @CacheEvict for fine-grained control over caching.

• Consider distributed caching solutions like Redis or Hazelcast for scalability across multiple instances.

• Cache external API responses to minimize latency and reduce the number of API calls...read more

Changing annotations on Spring Boot classes can have significant impact on the application.

• Changing annotations can affect the behavior of the application

• Annotations can control the lifecycle of beans, security, caching, etc.

• Removing or modifying annotations can cause runtime errors

• Adding new annotations can introduce new functionality

• Annotations can affect the performance of the application

Interview questions for Senior Java Developer

• List is an ordered collection, Set is an unordered collection with no duplicates, Map is a key-value pair collection

• Exception handling is used to handle runtime errors and prevent program crashes

• Throw is used to throw an exception explicitly, Throws is used to declare an exception that a method may throw

• Threads are used to execute multiple tasks simultaneously and improve program performance

• Marker interface is an interface with no ...read more

Marker interface is an interface with no methods, used to mark classes for special treatment.

• Marker interface is an empty interface with no methods

• It is used to mark classes for special treatment

• Examples include Serializable, Cloneable interfaces

Design a reliable messaging system using Kafka and RabbitMQ for communication between distributed components.

• Use Kafka for high-throughput, low-latency messaging with strong durability guarantees.

• Implement RabbitMQ for reliable message queuing and delivery.

• Integrate Kafka for real-time event streaming and RabbitMQ for asynchronous communication.

• Leverage Kafka Connect to easily connect Kafka with external systems and RabbitMQ plugins for enhanced functionality.

Key Java concepts including synchronization, execution order, design patterns, and SOLID principles.

• Synchronized Block: Locks a specific block of code, allowing more granular control over synchronization.

• Synchronized Method: Locks the entire method, which can lead to reduced concurrency.

• Performance: Synchronized blocks are generally better for performance as they allow more flexibility.

• Execution Order: Static blocks execute first, followed by the constructor, and then the mai...read more

Implement service discovery and load balancing using Netflix Eureka for microservices communication.

• Use Netflix Eureka as a service registry where microservices can register themselves and discover other services.

• Each microservice will have a Eureka client that registers its instance with the Eureka server upon startup.

• Eureka server provides a REST API for services to query for available instances of other services.

• Load balancing can be achieved using Ribbon, which integrates...read more

Designing a microservices architecture on AWS ECS involves containerization, service decomposition, and orchestration strategies.

• Identify and decompose the monolithic application into microservices based on business capabilities.

• Create Docker images for each microservice, ensuring they are lightweight and include only necessary dependencies.

• Use Docker Compose for local development to manage multi-container applications easily.

• Define ECS task definitions for each microservice,...read more

Java 8 introduced several new features including lambda expressions, functional interfaces, and streams.

• Lambda expressions allow for more concise and functional programming style.

• Functional interfaces enable the use of lambda expressions.

• Streams provide a powerful way to process collections of data in a functional manner.

• Default methods in interfaces allow for adding new methods to existing interfaces without breaking compatibility.

• Optional class helps to handle null values m...read more

Java 17 introduces sealed classes to restrict inheritance and improve code maintainability.

• Sealed classes are declared using the 'sealed' keyword followed by the permitted subclasses.

• Subclasses of a sealed class must be either final or sealed themselves.

• Errors may occur when trying to extend a sealed class with a non-permitted subclass.

Use Streams to remove duplicates and retain only even numbers from an array.

• Convert the array to a stream using Arrays.stream()

• Use distinct() to remove duplicates

• Filter out odd numbers using filter()

• Collect the result using collect(Collectors.toList())

Java versions 8, 11, and 17 have introduced various new features and improvements.

• Java 8 introduced lambda expressions, streams, and the new Date and Time API.

• Java 11 introduced local-variable syntax for lambda parameters, HTTP client API, and Flight Recorder.

• Java 17 introduced sealed classes, pattern matching for switch statements, and enhanced foreign function and memory API.

Program to filter employees using Java streams

• Create a list of employees

• Use stream() method to convert list to stream

• Use filter() method to filter employees based on condition

• Use collect() method to convert stream back to list

Immutable objects are those whose state cannot be changed after creation.

• Use final keyword to make class immutable

• Make all fields private and final

• Do not provide setter methods

• If a field is mutable, return a copy of it instead of the original object

• Examples: String, Integer, LocalDate

Implementing circuit breaker pattern in Spring Boot to handle failures in a distributed environment

• Use Spring Boot's resilience4j library to implement the circuit breaker pattern

• Configure the circuit breaker to monitor the external service dependency and trip open when failures exceed a certain threshold

• Handle the circuit breaker state transitions (OPEN, HALF_OPEN, CLOSED) appropriately in your code

• Implement fallback mechanisms to gracefully handle failures when the circuit b...read more