Tandem Crystals Senior Java Developer Interview Questions and Answers

Q1. Given an array {1, 2, 1, 4, 5, 4, 8, 7}, how can you use Streams to remove duplicates while retaining only the even numbers?
Ans. 
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())
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Q2. What is the use of Static and final when you will use Static methods
Ans. 
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 Ma
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Q3. What is the difference between @restController and @controller Annotation
Ans. 
The @RestController annotation is used to define RESTful web services while @Controller annotation is used to define MVC controller.
• RestController is a specialized version of Controller used for RESTful web services

• RestController eliminates the need for @ResponseBody annotation

• Controller is used for traditional MVC controller functionality

• RestController returns data directly without needing to go through a view resolve...read more
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Q4. What is microservices why we use it
Ans. 
Microservices are a software development technique where applications are composed of small, independent services that communicate with each other.
• Microservices allow for easier scalability and maintenance of complex applications.

• Each service in a microservices architecture can be developed, deployed, and scaled independently.

• Microservices promote flexibility and agility in software development.

• Examples of companies us...read more
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Q1. Project related questions, architecture, exception handling, Kafka use case.
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Q2. Oops question functional interface, marker interface.
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Q3. Memory leaks and how to avoid the same.
Ans. 
Memory leaks occur when a program allocates memory but does not release it, leading to inefficient memory usage.
• Use tools like profilers to identify memory leaks in Java applications.

• Avoid creating unnecessary objects and ensure proper garbage collection.

• Avoid static references to objects that can prevent them from being garbage collected.

• Close resources like files, database connections, and streams after use to preven
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Q4. Multi threading question
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Q1. Pom related questions how many scope available.
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Q2. Agile related questions
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Q3. Comparable vs comparator
Ans. 
Comparable is an interface used for natural ordering, while Comparator is an interface used for custom ordering.
• Comparable is implemented by the class itself to define the natural ordering of objects.

• Comparator is implemented by a separate class to define custom ordering of objects.

• Example: String class implements Comparable interface for natural ordering, while Collections class uses Comparator for custom sorting.
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The first round was an interview conducted with a GENAI virtual bot.

Q1. Internal architecture of Spring boot, how enable autoconfiguration works
Ans. 
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
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Q2. Questions mostly on microservices and coding question on restTemplate
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Q1. Basic question related to Java and spring boot
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Q1. Current Project role and responsibilites.
Ans. 
Leading a team of developers in designing and implementing a new web application for a financial services company.
• Managing a team of developers to ensure project milestones are met

• Designing the architecture of the web application

• Implementing new features and functionalities based on client requirements

• Conducting code reviews and providing technical guidance to team members
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Q1. Flow of micro services, annotations of boot
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Q2. Sorting program
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Q1. Project flow,team management
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Q2. Collection questions
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Q1. Normal hr questions,about changing jobs and etc.
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Q2. Salary negotiation
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Q1. Questions on Spring AOP
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Q2. How do Microservies talk to eachother
Ans. 
Microservices communicate with each other through APIs and messaging protocols.
• Microservices communicate via RESTful APIs, using HTTP requests and responses.

• Message brokers like Kafka or RabbitMQ are used for asynchronous communication between microservices.

• Service discovery tools like Eureka or Consul help microservices locate and communicate with each other.

• Microservices can also communicate through gRPC, a high-perf
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Q3. Logging framework used in current project
Ans. 
We are using Log4j2 for logging in the current project.
• Log4j2 is a popular logging framework in Java.

• It provides support for logging at different levels like DEBUG, INFO, WARN, ERROR, etc.

• Configuration can be done through XML, JSON, or properties file.

• Example: org.apache.logging.log4j log4j-api 2.14.1
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Q1. Write a program on java8 ?
Ans. 
Program using Java 8 features to filter a list of strings starting with 'A' and convert them to uppercase.
• Use Java 8 stream API to filter the strings starting with 'A'.

• Use map() function to convert the filtered strings to uppercase.

• Collect the results into a new list using collect() function.
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Q2. How connect two dbs in spring boot?
Ans. 
To connect two databases in Spring Boot, you can configure multiple data sources and use JPA to interact with them.
• Configure multiple data sources in application.properties or application.yml file

• Define multiple DataSource beans in your configuration class

• Use @Primary annotation to specify the primary data source

• Use @Qualifier annotation to specify which data source to use in a specific repository or service

• Use @Transa...read more
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Q3. Index in MySQL?
Ans. 
An index in MySQL is a data structure that improves the speed of data retrieval operations on a database table.
• Indexes are used to quickly locate rows in a table without having to search every row.

• They can be created on one or more columns in a table.

• Indexes can be unique, which means that the indexed columns must contain unique values.

• Examples of indexes include primary keys, unique keys, and regular indexes.
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Q4. Difference between post & get mapping in spring boot and can we update the data using post mapping?
Ans. 
Post mapping is used to create or update data, while get mapping is used to retrieve data. Yes, data can be updated using post mapping.
• Post mapping is used to create or update data in the server, while get mapping is used to retrieve data from the server.

• Post mapping is typically used for operations that modify data, such as creating a new resource or updating an existing one.

• Get mapping is used for operations that do ...read more
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Q5. Microservices design patterns?
Ans. 
Design patterns in microservices architecture help in solving common problems and improving scalability, maintainability, and flexibility.
• Service Registry pattern - used for service discovery and registration, such as Netflix Eureka

• Circuit Breaker pattern - prevents cascading failures by failing fast and providing fallback mechanisms, like Hystrix

• API Gateway pattern - acts as a single entry point for clients to access ...read more
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Q6. Explain about SOLID principles in java?
Ans. 
SOLID principles are a set of five design principles in object-oriented programming to make software designs more understandable, flexible, and maintainable.
• S - Single Responsibility Principle: A class should have only one reason to change.

• O - Open/Closed Principle: Classes should be open for extension but closed for modification.

• L - Liskov Substitution Principle: Objects of a superclass should be replaceable with obje...read more
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Q7. What are the advantages of spring boot over spring?
Ans. 
Spring Boot simplifies the development of Spring applications by providing out-of-the-box configurations and reducing boilerplate code.
• Spring Boot provides a quick and easy way to set up a Spring application with minimal configuration.

• It includes embedded servers like Tomcat, Jetty, or Undertow, eliminating the need for deploying WAR files.

• Auto-configuration feature in Spring Boot automatically configures the applicati...read more
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Q8. Give one API task and need to sort the employee or users data based on the interviewer requirement?
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Q1. What is final and finally
Ans. 
final is a keyword in Java used to declare constants, while finally is a block used in exception handling to ensure code is executed regardless of an exception.
• final keyword is used to declare constants in Java

• final variables cannot be reassigned once initialized

• finally block is used in exception handling to ensure code is executed regardless of an exception

• finally block is often used to release resources like closing
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Q2. Brief description about the last project
Ans. 
Developed a web application for a financial institution to manage customer accounts and transactions.
• Used Java Spring framework for backend development

• Implemented RESTful APIs for communication between frontend and backend

• Utilized Hibernate for database interaction

• Integrated third-party payment gateway for transactions
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