CMS Computers Limited (INDIA) Java Developer Interview Questions and Answers for Experienced

Q1. What is Functional interface
Ans. 
Functional interface is an interface with only one abstract method, used for lambda expressions.
• Functional interfaces can have multiple default or static methods, but only one abstract method.

• They are used for lambda expressions and method references in Java.

• Examples of functional interfaces in Java include Runnable, Callable, and Comparator.
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Q2. Java 8 features
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Q3. One Coding question based on String
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Q1. 1. How microservices communicate with each other?
Ans. 
Microservices communicate with each other through APIs and messaging protocols.
• Microservices use APIs to communicate with each other.

• Messaging protocols like HTTP, AMQP, and MQTT are used for asynchronous communication.

• Service discovery mechanisms like Eureka and Consul are used to locate services.

• API gateways like Zuul and Kong are used to manage API traffic.

• Event-driven architecture is used for real-time communicatio
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Q2. 2. How do you secure your APIs?
Ans. 
Securing APIs involves implementing authentication, authorization, encryption, and input validation.
• Implement authentication mechanisms like OAuth, JWT, or API keys

• Use authorization to control access to APIs based on user roles and permissions

• Encrypt sensitive data transmitted over the network using HTTPS

• Validate and sanitize input to prevent common security vulnerabilities like SQL injection or cross-site scripting (X
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Q3. 3. Scenario based question on qualifier?
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Q4. 4. What is ORM tool?
Ans. 
ORM (Object-Relational Mapping) tool is a software framework that maps objects to relational databases.
• ORM tool simplifies database operations by allowing developers to interact with databases using object-oriented programming.

• It eliminates the need for writing complex SQL queries by providing a higher-level abstraction.

• ORM tools handle tasks like data persistence, retrieval, and mapping between objects and database ta...read more
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Q5. 5. Advantages of hibernate
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Hibernate simplifies database programming in Java applications.
• Hibernate provides a simple and efficient way to interact with databases.

• It eliminates the need for writing complex SQL queries.

• It supports object-oriented programming and mapping of Java classes to database tables.

• It provides caching and lazy loading mechanisms for improved performance.

• It supports transaction management and reduces the risk of data corrupt...read more
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Q6. 6. Rest controller vs Controller
Ans. 
Rest controller is used for RESTful web services while Controller is used for traditional web applications.
• Rest controller maps HTTP requests to RESTful web services while Controller maps HTTP requests to traditional web applications.

• Rest controller uses @RestController annotation while Controller uses @Controller annotation.

• Rest controller returns data in JSON or XML format while Controller returns data in HTML format...read more
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Q7. 7. What if i write component in place of service ?
Ans. 
Using component instead of service may cause confusion and errors in the code.
• Components and services are two different concepts in Java development.

• Components are used for UI elements while services are used for business logic.

• Using component instead of service may lead to errors in the code and confusion for other developers.

• For example, if a component is used instead of a service for business logic, it may not have ...read more
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Q8. 8. What is the work of @autowired?
Ans. 
The @Autowired annotation is used to automatically wire beans by matching the data type of the bean with the data type of the property.
• Used to inject dependencies automatically

• Reduces the need for manual bean configuration

• Can be used with constructors, fields, and methods

• Can be used with @Qualifier to specify which bean to wire
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Q9. 9. What is Eureka server ? Default port
Ans. 
Eureka server is a service registry that enables microservices to discover and communicate with each other.
• Eureka server is a component of Netflix's OSS suite.

• It allows services to register themselves and discover other services.

• It uses a REST API for communication.

• Default port is 8761.
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Q10. 10. What is circuit breaker? Hystrix
Ans. 
Circuit breaker is a design pattern used to prevent cascading failures in distributed systems. Hystrix is a popular implementation.
• Circuit breaker monitors the availability of a service and trips if the service fails repeatedly.

• It helps to prevent cascading failures by failing fast and providing fallback options.

• Hystrix is a popular implementation of circuit breaker pattern in Java.

• It provides features like request cac
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Q11. 11. What are ternary operators ?
Ans. 
Ternary operators are conditional operators that evaluate a boolean expression and return one of two values based on the result.
• Ternary operators are written in the form of 'condition ? value1 : value2'

• If the condition is true, the operator returns value1, otherwise it returns value2

• Ternary operators can be used as a shorthand for if-else statements

• Example: int x = (a > b) ? a : b; // assigns the larger value of a and
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Q12. 12. How to write the entity class?
Ans. 
Entity class represents a table in a database and its attributes as fields.
• Define class with @Entity annotation

• Add @Id annotation to primary key field

• Add @Column annotation to map fields to table columns

• Implement getters and setters

• Override equals() and hashCode() methods
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Q13. 13. What is crud vs Jpa ?
Ans. 
CRUD is a basic operation for data manipulation while JPA is a Java specification for ORM.
• CRUD stands for Create, Read, Update, and Delete which are basic operations for data manipulation.

• JPA is a Java specification for Object-Relational Mapping (ORM) which provides a way to map Java objects to relational database tables.

• JPA provides a higher level of abstraction and simplifies the data access layer by providing an API...read more
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Q1. Difference between Hashset and Treeset
Ans. 
HashSet is an unordered collection while TreeSet is a sorted collection.
• HashSet uses hashing to store elements, allowing for constant time complexity for basic operations like add, remove, and contains.

• TreeSet uses a Red-Black tree to store elements in sorted order, allowing for log(n) time complexity for basic operations.

• HashSet does not maintain any order of elements while TreeSet maintains elements in sorted order.

• H...read more
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Q2. Final Finally and finalize difference
Ans. 
Final, finally, and finalize have different meanings in Java.
• final is a keyword used to declare constants or prevent inheritance

• finally is a block used in exception handling to execute code after try/catch

• finalize is a method used for cleanup operations before an object is garbage collected
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Q1. What are the differences between an ArrayList and a LinkedList?
Ans. 
ArrayList is implemented as a resizable array, while LinkedList is implemented as a doubly linked list.
• ArrayList provides fast random access and slower insertion/deletion, while LinkedList provides fast insertion/deletion and slower random access.

• ArrayList uses less memory overhead compared to LinkedList.

• Example: ArrayList is more suitable for scenarios where frequent access and traversal of elements is required, while...read more
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Q1. They asked some core Java Concepts,String,Java 8,SpringBoot Architecture,Stream API code
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Collection , logical

Q1. Opps ,spring boot
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Q2. Explain opps concept, what is spring boot
Ans. 
OOPs concept is a programming paradigm based on the concept of objects, Spring Boot is a framework for building Java applications.
• OOPs concept stands for Object-Oriented Programming, which focuses on creating objects that interact with each other to solve problems.

• It involves concepts like inheritance, encapsulation, polymorphism, and abstraction.

• Spring Boot is a framework that simplifies the development of Java applic...read more
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Q3. What is controller and rest controller
Ans. 
Controller is a class that handles user requests and returns appropriate response. Rest controller is a specialized controller for RESTful web services.
• Controller is a class in MVC architecture that handles user requests and interacts with the model and view.

• Rest controller is a specialized controller in Spring framework for building RESTful web services.

• Rest controller uses annotations like @RestController and @Reques...read more
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Q4. Internal working of hashmap
Ans. 
HashMap is a data structure that stores key-value pairs and uses hashing to efficiently retrieve values.
• HashMap internally uses an array of linked lists to store key-value pairs.

• When a key-value pair is added, the key is hashed to find the index in the array where it will be stored.

• If multiple keys hash to the same index, a linked list is used to handle collisions.

• HashMap allows null keys and values, but only one null ...read more
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Q5. Who is best jdbc or hibernate
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What is java
What' is object composition
What is class

Q1. What' is about your self
Ans. 
I am a Java Developer with 5 years of experience in developing web applications.
• I have a strong understanding of Java programming language and its frameworks like Spring and Hibernate.

• I have experience in developing RESTful APIs and integrating third-party APIs.

• I am proficient in database management using SQL and have worked with MySQL and Oracle databases.

• I have a good understanding of front-end technologies like HTML...read more
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Q2. What is javascript What is jdk What is while loop
Ans. 
Javascript is a scripting language used for web development. JDK is a Java Development Kit. While loop is a control flow statement.
• Javascript is used for client-side scripting, creating interactive web pages, and adding functionality to web applications.

• JDK is a software development kit used for developing Java applications.

• While loop is a control flow statement used to execute a block of code repeatedly as long as a s
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Q3. What is java What is object
Ans. 
Java is a high-level programming language used for developing applications. An object is an instance of a class.
• Java is platform-independent and can run on any device with a JVM.

• Java is an object-oriented language that supports encapsulation, inheritance, and polymorphism.

• Objects are created from classes and have properties and methods.

• Example: A car class can have objects like BMW, Audi, etc. with properties like colo
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