Verifone Front end Engineer Interview Questions and Answers

Ajax calls allow for asynchronous communication between client and server without reloading the page.

• Ajax stands for Asynchronous JavaScript and XML

• Uses XMLHttpRequest object to send and receive data

• Allows for partial page updates without reloading the entire page

• Can handle data in various formats such as JSON, XML, HTML, and plain text

• Example: $.ajax({url: 'example.com', success: function(data){console.log(data)}});

REST is lightweight and uses HTTP while SOAP is XML-based and has more features.

• REST uses HTTP methods like GET, POST, PUT, DELETE while SOAP uses XML messaging.

• REST is stateless while SOAP can maintain state.

• REST is faster and easier to use while SOAP is more secure and reliable.

• REST is used for web services while SOAP is used for enterprise-level services.

• Example of REST: Twitter API. Example of SOAP: Amazon Web Serv

GET and POST are HTTP methods used for sending data to a server.

• GET is used to retrieve data from a server

• POST is used to submit data to a server

• GET requests can be cached and bookmarked

• POST requests are not cached and cannot be bookmarked

• GET requests have length restrictions

• POST requests have no length restrictions

• GET requests are less secure than POST requests

Observer pattern is a design pattern in which an object maintains a list of its dependents and notifies them automatically of any state changes.

• Also known as publish-subscribe pattern

• Used in event-driven systems

• Allows loose coupling between objects

• Example: A weather station broadcasts weather updates to multiple displays

• Example: A stock market ticker notifies multiple investors of stock price changes

Singleton is a design pattern that restricts the instantiation of a class to a single object.

• Singleton ensures that only one instance of a class exists in the entire application.

• It provides a global point of access to the instance.

• Commonly used in scenarios where a single instance needs to coordinate actions across the system.

• Example: Database connection manager, logger, configuration manager.

Immutable in Java refers to objects whose state cannot be changed after creation.

• String, Integer, and other wrapper classes are immutable in Java.

• Immutable objects are thread-safe and can be shared without synchronization.

• To create an immutable class, make all fields final and private, and don't provide setters.

• Examples of immutable classes in Java include LocalDate, LocalTime, and LocalDateTime.

Creating immutable in Java

• Use final keyword to make variables immutable

• Use private constructor to prevent object modification

• Use defensive copying to prevent modification of mutable objects

• Use enum to create immutable objects

• Use String class to create immutable strings

Dependency injection is a design pattern that allows objects to receive dependencies rather than creating them internally.

• It helps to decouple the code and makes it more testable and maintainable.

• It allows for easier swapping of dependencies without changing the code.

• There are three types of dependency injection: constructor injection, setter injection, and interface injection.

• Example: Instead of creating a database co...read more

CORS stands for Cross-Origin Resource Sharing. It is a security feature implemented in web browsers to restrict access to resources from different origins.

• CORS allows web servers to specify which origins are allowed to access its resources

• It is implemented using HTTP headers

• CORS prevents malicious websites from accessing sensitive data from other websites

• Examples of resources that may be restricted by CORS include cook

CORS can be overcome by configuring the server to allow cross-origin requests.

• Configure the server to include the Access-Control-Allow-Origin header

• Use JSONP (JSON with Padding) to bypass CORS restrictions

• Use a proxy server to make the request on behalf of the client

• Use a browser extension to disable CORS restrictions during development

• Use a server-side proxy to forward requests to the target server

Race condition is a situation where multiple threads/processes access and manipulate shared data simultaneously.

• It can be eliminated by using synchronization techniques like locks, semaphores, and mutexes.

• Another way is to use atomic operations that ensure the data is accessed and modified atomically.

• Using thread-safe data structures can also prevent race conditions.

• Example: Two threads trying to increment a shared var...read more

JCube is a Java library for creating and manipulating Rubik's Cube puzzles.

• JCube provides classes for representing Rubik's Cube puzzles and algorithms for solving them.

• It supports various cube sizes and can generate random scrambles.

• JCube can be used in Java applications or as a standalone command-line tool.

• It is open source and available on GitHub.

Regression testing is the process of testing changes made to a software application to ensure that existing functionality still works.

• It is performed after making changes to the software

• It ensures that existing functionality is not affected by the changes

• It helps to catch any defects or bugs that may have been introduced

• It can be automated using testing tools

• Examples include retesting after bug fixes, testing after new

Software engineering principles are the best practices and guidelines for developing high-quality software.

• Software should be designed with modularity and scalability in mind.

• Code should be well-documented and easy to read.

• Testing and debugging should be an integral part of the development process.

• Version control should be used to manage code changes.

• Security and privacy should be considered throughout the development

A Singleton class is a class that can only have one instance at a time.

• It restricts the instantiation of a class to a single object.

• It provides a global point of access to that instance.

• It is often used in situations where a single object is required to coordinate actions across a system.

• Example: Database connection manager, Configuration manager, Logger manager.

Testing principles ensure software quality, while design principles guide software development.

• Testing principles include unit testing, integration testing, and acceptance testing.

• Design principles include SOLID, DRY, and KISS.

• Testing principles ensure that software meets requirements and is free of defects.

• Design principles guide software development to be modular, maintainable, and scalable.

I have the necessary skills, experience, and passion to contribute to VISA's success.

• I have a strong background in software development and have worked on projects similar to those at VISA.

• I am a quick learner and can adapt to new technologies and programming languages easily.

• I am passionate about creating high-quality software that meets the needs of users and exceeds their expectations.

• I am a team player and can work...read more

A profile that challenges me to learn and grow while allowing me to contribute to a team.

• A position that encourages continuous learning and development

• A role that allows me to collaborate with a team and contribute to projects

• A company culture that aligns with my values and work ethic

I am interested in exploring new opportunities and challenges that this company can offer.

• I am impressed with the company's reputation and growth potential.

• I am excited about the projects and technologies this company is working on.

• I believe this company can provide me with a better work-life balance and career growth opportunities.

• I am looking for a company culture that aligns with my values and goals.

• I am open to exp...read more

Autocomplete in IDEs helps developers write code faster by suggesting code snippets and completing code as they type.

• Autocomplete should suggest code snippets based on the context of the code being written

• Autocomplete should prioritize suggestions based on frequency of use

• Autocomplete should also suggest variable and function names

• Autocomplete should be customizable to allow for user-defined snippets and suggestions

• Exa...read more

My weakness is public speaking.

• I tend to get nervous when speaking in front of large groups.

• I am working on improving my public speaking skills by practicing and seeking feedback.

• I have taken courses and attended workshops to help me overcome my fear of public speaking.

Comparing 2 basketball game scenarios with different number of trials and baskets required to win

• Calculate the probability of winning in each game scenario using binomial distribution formula

• Compare the probabilities to determine which game scenario is preferable

• In game1, the probability of winning is p. In game2, the probability of winning is the sum of probabilities of making 2 or 3 baskets

• If p is high, game1 is pref...read more

Implement Binary Search Tree using given array of strings.

• Sort the array in ascending order

• Find the middle element and make it the root of the tree

• Recursively create left and right subtrees using the left and right halves of the array

• Repeat until all elements are added to the tree

Print the given Binary search tree in ascending order

• Traverse the left subtree recursively

• Print the root node

• Traverse the right subtree recursively

Find buy and sell points for maximum profit in an array of stock prices in O(n)

• Iterate through the array and keep track of the minimum price seen so far

• Calculate the profit at each index by subtracting the minimum price from the current price

• Update the maximum profit and buy/sell points accordingly

• Return the buy and sell points for maximum profit

Chennai faces problems related to water scarcity, traffic congestion, and pollution.

• Water scarcity due to inadequate rainfall and poor management of water resources.

• Traffic congestion due to the increasing number of vehicles and poor road infrastructure.

• Pollution caused by industries, vehicular emissions, and improper waste disposal.

Need more context on the question to provide an answer.

• Please provide more information on the problem to be solved.

• Without context, it is difficult to provide a solution.

• Can you please provide more details on the problem statement?

Visa is a global payments technology company that connects consumers, businesses, banks and governments in more than 200 countries and territories.

• Visa operates the world's largest retail electronic payments network.

• VisaNet, the company's global processing system, handles more than 65,000 transaction messages a second.

• Visa is constantly innovating to improve payment security and convenience, with initiatives such as Vi...read more