Marolix Technology Solutions Senior Java Developer Interview Questions and Answers

Q1. Difference between HashMap and TreeMap? Internal working of HashMap?
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Q2. Functional Interface?
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Q3. Singleton Class?
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Q4. What is Eureka Server?
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Q5. How to handle Exception in SpringBoot?
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Q6. Find the average sal of employee in each department using java 8 Stream?
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Q7. What is circuit Breaker?
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Q8. What is docker and kubernates?
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Q1. Core Java questions and multithreading basics like executor service
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Q2. Spring boot error handling, simple questions on distributed systems
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Q3. Coding question. Requested to do in O(n ) time complexity as oppsed to O(n2) suggested by me.
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Q1. Given an array find all the numbers whose sum is 11 using streams only
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Q2. Spring boot basics, hibernate queries, what is native query
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Q1. Design patterns in Java, write a singleton class
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Q2. Spring IOC and AOP
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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
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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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Q1. What are intermediate and terminal operations
Ans. 
Intermediate operations transform the elements of a stream, while terminal operations produce a result or side-effect.
• Intermediate operations include map, filter, sorted, distinct, etc.

• Terminal operations include forEach, collect, reduce, count, etc.

• Intermediate operations are lazy and do not execute until a terminal operation is called.

• Terminal operations trigger the processing of the stream and produce a result.
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Q2. Predefined functional interface
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Q3. Ways to create Thread
Ans. 
Ways to create Thread in Java
• Extending the Thread class

• Implementing the Runnable interface

• Using Executor framework
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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. 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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There were MCQ questions consists of different sections like Design Pattern,Java 8

Q1. Questions related to Multithreading,Design patterns
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Q2. Java coding questions
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Q1. Questions related to Multithreading
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Q2. Java coding questions
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