20+ Einfochips Interview Questions and Answers

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

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.

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

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

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.

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

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

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

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.

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

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

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

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

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 }

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

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

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

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

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