Verifone Senior QA Engineer Interview Questions and Answers

MongoDB is scalable due to its ability to horizontally partition data across multiple servers.

• MongoDB uses sharding to distribute data across multiple servers.

• Sharding allows for horizontal scaling by adding more servers to the cluster.

• MongoDB also supports replica sets for high availability and fault tolerance.

• Indexes can be created on any field in a MongoDB document, allowing for efficient querying of large datasets.

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...read more

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...read more

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

My biggest achievement till date is successfully leading a team to develop and launch a new software product ahead of schedule.

• Led a team of developers to create a new software product

• Completed the project ahead of schedule

• Received positive feedback from clients and stakeholders

I would address conflicts directly and respectfully, seeking to understand the root cause and find a mutually beneficial solution.

• Listen actively to understand the other person's perspective

• Communicate clearly and respectfully

• Identify the root cause of the conflict

• Brainstorm potential solutions together

• Be willing to compromise and find a mutually beneficial solution

Success is achieving personal goals, feeling fulfilled, and making a positive impact.

• Success is subjective and can vary from person to person.

• It involves setting and achieving goals, both short-term and long-term.

• Feeling fulfilled and content with one's accomplishments is a key aspect of success.

• Making a positive impact on others or the world can also be a measure of success.

• Success is not just about material wealth or...read more

Dijkstra's algorithm finds the shortest path between nodes in a graph.

• Create a graph with nodes and edges

• Assign a tentative distance to each node

• Set the initial node as current and mark it visited

• For each neighbor of the current node, calculate the tentative distance

• If the tentative distance is less than the current distance, update the distance

• Mark the current node as visited and select the unvisited node with the sma...read more

A program to reverse a singly linked list

• Create a new empty linked list

• Traverse the original linked list and insert each node at the beginning of the new list

• Return the new list

Methods to find nth largest element in an unsorted linked list

• Traverse the linked list and store elements in an array, sort the array and return the nth largest element

• Use quickselect algorithm to find the nth largest element in O(n) time complexity

• Implement a max heap and extract the nth largest element

• Divide the linked list into smaller sublists and recursively find the nth largest element

• Use merge sort to sort the l...read more

A prime number is a number that is divisible only by 1 and itself.

• A prime number has exactly two factors: 1 and itself.

• Prime numbers cannot be divided evenly by any other number.

• Examples of prime numbers include 2, 3, 5, 7, 11, 13, 17, etc.

Test cases for a bank transaction

• Transaction amount within account balance limit

• Transaction amount exceeds account balance limit

• Transaction to a valid account number

• Transaction to an invalid account number

• Transaction with correct transaction code

• Transaction with incorrect transaction code

• Transaction during bank working hours

• Transaction outside bank working hours

Design classes for educational institutions in a city

• Identify the main entities: schools, students, teachers, courses

• Create a School class with attributes like name, address, and a list of students and teachers

• Create a Student class with attributes like name, age, and a list of courses

• Create a Teacher class with attributes like name, specialization, and a list of courses

• Create a Course class with attributes like name, ...read more