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

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

DELETE removes specific rows from a table, while TRUNCATE removes all rows and resets auto-increment values.

• DELETE is a DML command, while TRUNCATE is a DDL command.

• DELETE can be rolled back, while TRUNCATE cannot be rolled back.

• DELETE triggers delete triggers, while TRUNCATE does not trigger them.

• DELETE is slower as it logs individual row deletions, while TRUNCATE is faster as it logs the deallocation of the data pages.

• Example: DELETE FROM table_name WHERE condition; TRUNCAT...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

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

Choose AWS for flexibility and customization, choose Dynamo DB for simplicity and scalability

• Consider AWS if you need more flexibility and customization in your data storage solution

• Choose Dynamo DB if you prioritize simplicity and scalability for your mission critical application

• AWS offers a wide range of services and configurations for high availability and scalability, while Dynamo DB is a fully managed NoSQL database service that can automatically scale based on demand

• If ...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

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

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

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

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.

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

Dependency Injection is a design pattern where the dependencies of an object are provided externally rather than created within the object itself.

• Types of Dependency Injection: Constructor Based, Setter Based, Field Injection

• Constructor Based: Dependencies are provided through the constructor of the class

• Setter Based: Dependencies are provided through setter methods

• Field Injection: Dependencies are directly assigned to fields of the class

Springboot is a framework that simplifies the development of Java applications by providing pre-configured settings and conventions.

• Springboot is built on top of the Spring framework, providing a more streamlined way to build Spring applications.

• Springboot eliminates the need for XML configuration files and allows for easier setup of dependencies.

• Difference between @Component and @ComponentScan: @Component is used to mark a class as a Spring component, while @ComponentScan is...read more

Implement pagination in UI by limiting results to 10 per page.

• Implement pagination logic in UI to display 10 results per page.

• Use backend query parameters like 'offset' and 'limit' to fetch specific results.

• Utilize front-end frameworks like React or Angular for efficient pagination implementation.

Monolith is a single, large application while microservices are smaller, independent services. Microservices are better for scalability and flexibility.

• Monolith is a single, large application where all components are tightly coupled. Microservices are smaller, independent services that communicate with each other through APIs.

• Monoliths are easier to develop and deploy initially but become harder to maintain and scale as they grow. Microservices allow for better scalability an...read more

Garbage Collection in Java is the process of automatically reclaiming memory by destroying unused objects.

• Garbage Collection is a process in Java where the JVM automatically reclaims memory by destroying objects that are no longer referenced.

• The process of GC involves marking objects that are still in use, sweeping and deleting objects that are no longer in use, and compacting the memory to reduce fragmentation.

• We can explicitly invoke Garbage Collector in Java using System.g...read more

Spring Boot uses @Primary annotation to determine which data source to use when multiple are available.

• Spring Boot uses the @Primary annotation to specify the primary bean to be used when multiple beans of the same type are present.

• If no specific profile is defined, Spring Boot will use the bean marked with @Primary as the default data source.

• Developers can also use @Qualifier annotation to specify which bean to use if @Primary is not defined.

Garbage collector in Java is a built-in mechanism that automatically manages memory by reclaiming unused objects.

• Garbage collector runs in the background to reclaim memory from objects that are no longer in use.

• It helps prevent memory leaks and optimize memory usage.

• Examples of garbage collectors in Java include Serial, Parallel, CMS, G1, and Z Garbage Collectors.

Singleton is a design pattern that restricts the instantiation of a class to one object.

• To create a singleton class, make the constructor private, create a static method to get the instance of the class, and create a private static variable to hold the instance.

• Benefits of singleton include ensuring only one instance of the class exists, providing a global point of access to the instance, and reducing the number of objects created in the system.

• Example: java.lang.Runtime is a...read more

SQL questions on Truncate, Delete, Drop, Composite Key and Query to find customer details

• Truncate removes all data from a table, Delete removes specific data, Drop removes the entire table

• Composite key is a combination of two or more columns that uniquely identifies a row in a table

• SELECT * FROM customer c JOIN order o ON c.customer_id = o.customer_id WHERE AVG(o.amount) BETWEEN 1000 AND 2000

Complexity analysis and optimization of algorithms for performance and scalability.

• Determine the time complexity (Big O notation) and space complexity of the algorithm.

• Identify bottlenecks and optimize code by reducing unnecessary operations or improving data structures.

• Use efficient algorithms and data structures like hash maps, binary search trees, and dynamic programming.

• Parallelize tasks to leverage multi-core processors for improved performance.

• Consider scalability by de...read more

Handle out-of-memory exception by analyzing heap dump and optimizing code.

• Analyze heap dump to identify memory leaks

• Optimize code to reduce memory usage

• Increase heap size if necessary

• Use memory profiling tools like JProfiler or VisualVM

• Avoid creating unnecessary objects

• Use caching to reduce object creation

• Implement garbage collection strategies

equals and hashcode are methods in Java used for comparing objects and generating hash codes respectively. Object class does implement equals method.

• equals method is used to compare two objects for equality. It is overridden in most classes to provide custom comparison logic.

• hashcode method is used to generate a unique integer value for an object. It is used in hash-based collections like HashMap.

• Object class does implement equals method, but it uses reference equality (==) f...read more

The system or process of a software company involves various stages from planning to deployment.

• The process starts with requirement gathering and analysis.

• Then comes the design and development phase.

• Testing and quality assurance is an important part of the process.

• Deployment and maintenance are the final stages.

• Agile and DevOps methodologies are commonly used.

• Tools like JIRA, Git, Jenkins, etc. are used for project management and automation.

Shallow and deep comparison in Strings with code example

• Shallow comparison checks if two String variables refer to the same object in memory

• Deep comparison checks if two String variables have the same sequence of characters

• Shallow comparison can be done using the '==' operator

• Deep comparison can be done using the 'equals()' method

• Example: String str1 = 'hello'; String str2 = 'hello'; str1 == str2; //shallow comparison returns true

• Example: String str1 = 'hello'; String str2 = ...read more

Spring Boot uses autoconfiguration to automatically configure the Spring application based on dependencies and properties.

• Spring Boot autoconfiguration is achieved through @EnableAutoConfiguration annotation

• Autoconfiguration classes are located in the org.springframework.boot.autoconfigure package

• Autoconfiguration classes are conditionally applied based on the presence of specific classes or properties

Answering questions related to Java development and architecture

• Monolithic architecture is a traditional approach where all components of an application are tightly coupled into a single unit

• Microservices architecture is a modern approach where an application is divided into smaller, loosely coupled services

• Singleton class is a design pattern that restricts the instantiation of a class to a single object

• Static variables in Singleton class are shared among all instances and ca...read more

A set of interview questions for a Senior Java Developer position.

• Singleton class in Java is a class that allows only one instance of itself to be created.

• String is immutable in Java because it ensures thread safety and allows for efficient memory management.

• ArrayList and LinkedList are both implementations of the List interface, but differ in their underlying data structure and performance characteristics.

• IOC (Inversion of Control) in Spring is a design principle that allows...read more

Constructor or Setter based injection is used in Spring framework to inject dependencies into a bean.

• Constructor injection involves passing dependencies as arguments to the constructor of a class.

• Setter injection involves setting dependencies using setter methods.

• Constructor injection is preferred for mandatory dependencies, while setter injection is used for optional dependencies.

• Example: Constructor injection - public class MyClass { private Dependency dependency; public My...read more

Meta space is a memory space in Java that stores metadata about classes and methods.

• Meta space replaces the permanent generation in Java 8 and earlier versions.

• In Java 11, meta space is improved by introducing a new flag called 'UseContainerSupport' which allows the JVM to use container-specific memory limits.

• This improvement helps in better managing memory usage in containerized environments.

To set up a Spring-Boot project with only OS and JDK, you need to install Maven and then create a new project using Spring Initializr.

• Install Apache Maven to manage dependencies and build the project

• Use Spring Initializr to generate a new Spring Boot project with required dependencies

• Import the project into your IDE and start coding

The question asks to multiply all elements in an array except for a given number.

• Iterate through the array and calculate the product of all elements except the given number.

• Use a variable to keep track of the product.

• If the given number is 1, multiply all other elements.

• Return the resulting array.

Static methods can be accessed without creating an instance of the class, while final keyword makes the method unchangeable.

• Static methods belong to the class itself, not to any specific instance

• Final keyword ensures that the method cannot be overridden in subclasses

• Static methods are commonly used for utility methods that do not require access to instance variables

• Example: Math class in Java has static methods like Math.max() and Math.min()

The default server in a Spring Boot application is Tomcat. Other servers can be configured by adding dependencies and modifying the configuration.

• The default server in Spring Boot is Tomcat, but other servers like Jetty or Undertow can be used.

• To configure a different server, you need to exclude the default server dependency and add the desired server dependency in the pom.xml file.

• You also need to modify the application.properties or application.yml file to specify the serve...read more