Capgemini Senior Java Developer Interview Questions and Answers

HashMap is unordered, uses hashing for key-value pairs. TreeMap is ordered, uses Red-Black tree for key-value pairs.

• HashMap uses hashing to store key-value pairs, allowing for O(1) retrieval time on average.

• TreeMap uses Red-Black tree to store key-value pairs, maintaining order based on keys.

• HashMap allows one null key and multiple null values, while TreeMap does not allow null keys.

• Example: HashMap<String, Integer&...read more

A functional interface in Java is an interface with a single abstract method, enabling lambda expressions and method references.

• A functional interface can have multiple default or static methods.

• Common examples include Runnable, Callable, and Comparator.

• It is annotated with @FunctionalInterface for clarity.

• Lambda expressions can be used to instantiate functional interfaces.

A Singleton Class ensures a class has only one instance and provides a global point of access to it.

• Singleton pattern restricts instantiation of a class to one object.

• It is commonly used for logging, driver objects, caching, and thread pools.

• Example in Java: Use a private constructor and a static method to get the instance.

• Thread-safe implementation can be achieved using synchronized methods or double-checked locking.

Eureka Server is a service registry for microservices in a cloud environment.

• Eureka Server is part of Netflix OSS and allows microservices to register themselves and discover other services.

• It helps in load balancing and failover of services by keeping track of available instances.

• Eureka Server uses a REST API for communication between services and the server.

• Example: Microservices A, B, and C register themselves with ...read more

Exception handling in SpringBoot involves using @ExceptionHandler, @ControllerAdvice, and global exception handling.

• Use @ExceptionHandler annotation in controller classes to handle specific exceptions.

• Use @ControllerAdvice annotation to define global exception handling for all controllers.

• Implement a custom exception handler class to handle exceptions globally.

• Use ResponseEntity to return custom error messages and stat...read more

Calculate average salary of employees in each department using Java 8 Stream.

• Use Java 8 Stream to group employees by department

• Calculate average salary for each department using Stream's 'collect' method

• Use 'Collectors.averagingDouble' to calculate average salary

Circuit Breaker is a design pattern used in software development to prevent cascading failures in distributed systems.

• Circuit Breaker monitors the health of a service and stops sending requests if the service is not responding properly.

• It helps in improving the resilience of the system by providing a fallback mechanism when a service is down.

• Circuit Breaker can be configured with thresholds for error rates or response ...read more

Docker is a platform for developing, shipping, and running applications in containers. Kubernetes is an open-source system for automating deployment, scaling, and management of containerized applications.

• Docker allows developers to package applications and dependencies into containers for easy deployment and scalability.

• Kubernetes helps in automating the deployment, scaling, and management of containerized applications...read more

Map transforms elements, while flatMap flattens nested structures and then transforms them.

• map() applies a function to each element, returning a new stream of transformed elements.

• Example: [1, 2, 3].map(x -> x * 2) results in [2, 4, 6].

• flatMap() applies a function that returns a stream for each element, then flattens the result.

• Example: [1, 2].flatMap(x -> Stream.of(x, x * 2)) results in [1, 2, 2, 4].

• Use map when...read more

Use Java 8 Streams to find the first non-repeating character in a string efficiently.

• Utilize a Map to count character occurrences: `Map<Character, Long> charCount = str.chars().mapToObj(c -> (char) c).collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));`

• Filter the characters based on their count: `charCount.entrySet().stream().filter(entry -> entry.getValue() == 1)`.

• Find the first non...read more

Autowiring is a Spring framework feature that automatically injects dependencies into beans without explicit configuration.

• Autowiring can be done using annotations like @Autowired, @Inject, or @Resource.

• It simplifies dependency management by reducing boilerplate code.

• Example: Using @Autowired on a constructor allows Spring to automatically provide the required dependencies.

• There are different modes of autowiring: byTyp...read more

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.

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

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.

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

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

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

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

Implement a REST API to sort employee data based on various criteria like name, age, or salary.

• Use Spring Boot to create a RESTful API.

• Define an Employee class with fields like id, name, age, and salary.

• Implement a GET endpoint '/employees' that accepts query parameters for sorting.

• Use Java's Comparator to sort the list based on the specified field.

• Example: /employees?sort=name or /employees?sort=age