Fullstack Java Application Developer
40+ Fullstack Java Application Developer Interview Questions and Answers

Asked in Accenture

Q. Which authentication methods are used to secure REST APIs?
Various authentication methods can be used to secure REST API, including OAuth, JWT, Basic Authentication, and API Keys.
OAuth is a popular authentication method that allows users to grant access to third-party applications without sharing their credentials.
JWT (JSON Web Tokens) is a stateless authentication mechanism that uses a token to authenticate users.
Basic Authentication uses a username and password to authenticate users.
API Keys are unique identifiers that are used to ...read more

Asked in Accenture

Q. Which data structures are used in arrays and hashmaps?
Arrays use a linear data structure while HashMap uses a key-value pair data structure.
Arrays are indexed collections of elements of the same data type.
HashMaps store key-value pairs and allow for fast retrieval of values based on their keys.
Arrays have a fixed size while HashMaps can dynamically resize.
Arrays are more efficient for simple data structures while HashMaps are better for complex data structures.
Fullstack Java Application Developer Interview Questions and Answers for Freshers

Asked in Accenture

Q. Write a program to find duplicate elements in an ArrayList.
Program to find duplicate elements in an array list
Create a HashSet to store unique elements
Loop through the array list and add each element to the HashSet
If an element already exists in the HashSet, it is a duplicate
Add the duplicate element to another list or print it

Asked in Accenture

Q. What is the difference between getSession() and load() in Hibernate?
getSession() retrieves the current session while load() method loads the object by its identifier.
getSession() method is used to retrieve the current session from the session factory.
load() method is used to load the object by its identifier.
getSession() method returns null if there is no current session.
load() method throws an exception if the object is not found in the database.
getSession() method is used for read and write operations while load() method is used for read-on...read more

Asked in Volkswagen Group Technology Solution

Q. How do microservices communicate with each other?
Microservices can communicate with each other through synchronous HTTP calls, asynchronous messaging, or using a message broker.
Synchronous communication: Microservices can communicate directly through HTTP requests, such as REST APIs.
Asynchronous communication: Microservices can use messaging protocols like RabbitMQ or Kafka to send and receive messages.
Message broker: Microservices can communicate through a message broker like Apache Kafka, which acts as an intermediary for...read more

Asked in Accenture

Q. What are idempotent methods in REST?
Idempotent methods in REST are HTTP methods that can be repeated multiple times without changing the result beyond the initial application.
Idempotent methods are safe to retry or repeat without causing unintended side effects.
GET, HEAD, PUT, and DELETE are idempotent methods.
POST is not idempotent because it creates a new resource with a new URI each time it is called.
Idempotency is important for ensuring the reliability and consistency of RESTful APIs.
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Asked in CGI Group

Q. How would you improve the performance of a running application?
To improve the performance of a running application, consider optimizing code, database queries, caching, and server resources.
Optimize code by identifying and fixing bottlenecks, reducing unnecessary loops, and improving algorithms.
Optimize database queries by using indexes, avoiding unnecessary joins, and limiting the amount of data retrieved.
Implement caching mechanisms to store frequently accessed data in memory, reducing the need to fetch it from the database repeatedly....read more

Asked in CGI Group

Q. What are the different design patterns and how have you implemented them in projects?
I have implemented design patterns like Singleton, Factory, and Observer in various projects.
Implemented Singleton pattern to ensure only one instance of a class exists.
Utilized Factory pattern to create objects without specifying the exact class of object that will be created.
Used Observer pattern to establish a one-to-many dependency between objects, so that when one object changes state, all its dependents are notified and updated automatically.
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Asked in Accenture

Q. what is hql? what are it's benefits?
HQL stands for Hibernate Query Language. It is an object-oriented query language used to retrieve data from a database.
HQL is similar to SQL but uses object-oriented concepts like inheritance, polymorphism, and association.
It is database independent and can be used with any database supported by Hibernate.
HQL queries are compiled to SQL queries at runtime, which makes it more efficient than using SQL directly.
It supports caching and lazy loading, which can improve performance...read more

Asked in Accenture

Q. How do we handle exceptions in REST APIs?
Exceptions in REST are handled using try-catch blocks and HTTP status codes.
Use try-catch blocks to catch exceptions thrown by the application
Map exceptions to appropriate HTTP status codes
Return error messages in the response body
Use global exception handlers to handle uncaught exceptions
Avoid returning sensitive information in error messages

Asked in Accenture

Q. What are the methods of the Object class?
Methods of Object class in Java
toString() - returns a string representation of the object
equals(Object obj) - checks if two objects are equal
hashCode() - returns a hash code value for the object
getClass() - returns the runtime class of the object
wait() - causes the current thread to wait
notify() - wakes up a single thread that is waiting on the object
notifyAll() - wakes up all threads that are waiting on the object

Asked in Accenture

Q. What is the difference between String and StringBuffer?
String is immutable while StringBuffer is mutable.
StringBuffer is faster for concatenation operations.
StringBuffer has methods to modify the string while String does not.
StringBuffer is thread-safe while String is not.
Example: String str = "hello"; StringBuffer sb = new StringBuffer(str); sb.append(" world");
Example: String str = "hello"; str.concat(" world"); // returns a new string, original string is not modified.

Asked in Accenture

Q. What is the relationship between the hashCode and equals methods?
Hashcode and equals method are related in Java to ensure proper object comparison and hashing.
The hashcode method returns an integer value that represents the object's unique identifier.
The equals method compares two objects for equality and returns a boolean value.
If two objects are equal, their hashcodes must be equal as well.
If two objects have the same hashcode, it does not necessarily mean they are equal.
It is important to override both methods when creating custom class...read more

Asked in Raja Software Labs

Q. Given a string, find the first non-repeating character in it.
To find the first non-repeating character in a string, we can use a frequency count to identify unique characters efficiently.
Frequency Count: Use a hash map or dictionary to count occurrences of each character in the string.
Iterate Through String: After counting, iterate through the string again to find the first character with a count of 1.
Example: For the string 'swiss', the frequency count would be {'s': 3, 'w': 1, 'i': 1}. The first non-repeating character is 'w'.
Edge Ca...read more

Asked in CitiusTech

Q. What is a singleton class and how do you implement it?
Singleton class is a class that can only have one instance and provides a global point of access to it.
Singleton class restricts the instantiation of a class to one object.
It provides a way to access its unique instance globally.
Commonly used in scenarios where only one instance of a class is needed, such as database connections or thread pools.

Asked in Deloitte

Q. How do you use joins in Spring Boot?
Joins in Spring Boot are used to retrieve data from multiple tables in a database using relationships between them.
Use @Query annotation with JPQL or native SQL to perform joins in Spring Boot repositories
Specify the join condition in the query using ON keyword
Use JOIN FETCH to eagerly fetch associated entities in a single query

Asked in Carwale

Q. Difference between streams and for loop, Java coding optimization
Streams provide a functional approach to processing collections, while for loops offer imperative control over iteration.
Streams support functional programming, allowing operations like map, filter, and reduce.
For loops provide more control over iteration, including index manipulation.
Example of stream: List<String> names = Arrays.asList('Alice', 'Bob'); names.stream().filter(n -> n.startsWith('A')).forEach(System.out::println);
Example of for loop: for (String name : names) {...read more

Asked in CGI Group

Q. How is exception handling implemented in inheritance?
Exceptions in inheritance are handled using try-catch blocks in the subclass.
Inherited methods can throw exceptions that need to be caught in the subclass.
Subclass can override superclass methods and handle exceptions differently.
Superclass methods can declare checked exceptions that subclasses must handle.
Exceptions can be rethrown or wrapped in a new exception in the subclass.

Asked in Birlasoft

Q. Given an array, find the frequency of each duplicate element.
Find duplicate element frequency in an array of strings.
Create a HashMap to store each element and its frequency.
Iterate through the array and update the frequency in the HashMap.
Print out elements with frequency greater than 1.

Asked in Accenture

Q. How do you perform XML validation?
XML validation can be done using XML Schema Definition (XSD) or Document Type Definition (DTD).
XSD is the preferred method for XML validation as it provides more features and is easier to use.
DTD is an older method and has limited features compared to XSD.
XML validation can be done using tools like XMLSpy, Notepad++, and online validators like W3C Markup Validation Service.
Validation can be done programmatically using libraries like JAXB, SAX, and DOM in Java.
Validation error...read more

Asked in Accenture

Q. How do you secure a REST API?
Secure REST API using authentication, encryption, and authorization.
Use HTTPS protocol to encrypt data in transit
Implement authentication using tokens or OAuth2
Implement authorization using roles and permissions
Use input validation and output encoding to prevent injection attacks
Implement rate limiting to prevent DDoS attacks

Asked in Temenos

Q. What is SQL injection?
SQL injection is a type of cyber attack where malicious SQL statements are inserted into an entry field to manipulate the database.
SQL injection can be used to steal sensitive information, modify or delete data, or even take control of the entire database.
It can be prevented by using parameterized queries, input validation, and limiting user privileges.
Example: Entering ' OR 1=1;--' in a login form can bypass authentication and grant access to the system.
Example: Entering 'DR...read more

Asked in Accenture

Q. What is the synchronized keyword?
Synchronized keyword is used to control access to shared resources in a multithreaded environment.
It ensures that only one thread can access the shared resource at a time.
It can be applied to methods or blocks of code.
It can cause performance issues if used excessively.
Example: synchronized void myMethod() { //code }
Example: synchronized(this) { //code }

Asked in Baxter Planning

Q. How do you conduct code reviews?
Code reviews ensure code quality, maintainability, and knowledge sharing among team members.
Establish clear guidelines: Define coding standards and best practices for consistency.
Use tools: Leverage tools like GitHub or Bitbucket for pull requests and inline comments.
Focus on readability: Ensure code is easy to read and understand; for example, use meaningful variable names.
Check for functionality: Verify that the code meets the requirements and passes all tests.
Encourage con...read more

Asked in Accenture

Q. Describe the Reflection API in Java.
Reflection API in Java allows inspection and modification of runtime behavior of a program.
Reflection API provides classes like Class, Method, Field, Constructor, etc. to inspect and modify the behavior of a program at runtime.
It can be used to access private fields and methods of a class.
It can be used to create new instances of a class dynamically.
It can be used to invoke methods of a class dynamically.
It can be used to get information about the class hierarchy and interfac...read more

Asked in Accenture

Q. What is the difference between PUT and POST requests?
PUT is used to update an existing resource, while POST is used to create a new resource.
PUT replaces the entire resource with the new data, while POST appends the new data to the existing resource.
PUT is idempotent, meaning multiple identical requests will have the same effect as a single request, while POST is not.
PUT requires the client to specify the resource ID in the request URL, while POST does not.
Example: PUT /users/123 updates the user with ID 123, while POST /users ...read more

Asked in Accenture

Q. Describe cascading in Hibernate.
Cascading in Hibernate refers to the ability to propagate the state of an entity to its associated entities.
Cascading is used to automatically persist, update, or delete associated entities when the state of the parent entity changes.
There are different types of cascading options available in Hibernate, such as ALL, PERSIST, MERGE, REMOVE, and REFRESH.
For example, if a parent entity has a collection of child entities and the cascading option is set to ALL, then any changes ma...read more

Asked in Accenture

Q. Describe the caching mechanism in Hibernate.
Hibernate provides two levels of caching: first-level cache and second-level cache.
First-level cache is enabled by default and is associated with a Session object.
Second-level cache is optional and can be configured to use different caching providers like Ehcache, Hazelcast, etc.
Caching can improve application performance by reducing the number of database queries.
Caching can also cause data inconsistency issues if not used properly.
Hibernate provides annotations like @Cachea...read more

Asked in Accenture

Q. Types of cloning in java
There are two types of cloning in Java: Shallow and Deep cloning.
Shallow cloning creates a new object with the same field values as the original object, but the fields refer to the same objects as the original object.
Deep cloning creates a new object with the same field values as the original object, but the fields refer to new copies of the original objects.
Shallow cloning can be done using the clone() method, while deep cloning requires custom implementation.
Shallow cloning...read more

Asked in Atos

Q. What are the use cases for Java?
Java is a versatile programming language used for developing a wide range of applications, from web and mobile apps to enterprise systems.
Java is used for developing web applications, mobile applications, desktop applications, and enterprise systems.
It is commonly used in backend development for server-side programming.
Java is also used in game development, scientific applications, and big data processing.
It is platform-independent, meaning Java programs can run on any device...read more
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