EPAM Systems .NET Full Stack Interview Questions & Answers
Curated interview practice questions with answers. These are practice scenarios, not a verified list of past interview questions.
About EPAM Systems hiring for .NET Full Stack roles
EPAM Systems is a global digital platform engineering and software development services company. It works on product development, quality engineering, cloud and data projects for clients in finance, life sciences, retail and software. Its India delivery centres hire for software engineers, test automation engineers, data engineers and data scientists.
For .NET Full Stack roles, this EPAM Systems practice set focuses most on C# Fundamentals (7), SQL Server and T-SQL (6), ASP.NET Core Web API (5), Angular and React Front End (4). It has 15 easy, 12 medium, 3 hard questions, so you can start easy and work up to the harder ones.
Company type
IT services
Headquarters
Newtown, Pennsylvania, USA
Main India offices
Hyderabad, Bengaluru, Pune, Chennai, Gurugram
EPAM Systems .NET Full Stack interview process
Online coding assessment
Technical interview
Technical or design round
Hiring manager round
Typical pattern based on public candidate experiences. Rounds vary by role, team and year.
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01
Write a SQL Server query to find the second highest salary.
-- using DENSE_RANK (handles ties)
SELECT Salary
FROM (
SELECT Salary, DENSE_RANK() OVER (ORDER BY Salary DESC) AS rnk
FROM Employees
) t
WHERE rnk = 2;
-- using OFFSET
SELECT DISTINCT Salary
FROM Employees
ORDER BY Salary DESC
OFFSET 1 ROW FETCH NEXT 1 ROW ONLY;
Change 2 to N for the Nth highest salary.
02
How do you use an explicit transaction in EF Core across multiple SaveChanges calls?
await using var tx = await db.Database.BeginTransactionAsync();
try
{
db.Orders.Add(order);
await db.SaveChangesAsync();
var stock = await db.Stocks.SingleAsync(s => s.ProductId == order.ProductId);
stock.Quantity -= order.Quantity;
await db.SaveChangesAsync();
await tx.CommitAsync();
}
catch
{
await tx.RollbackAsync();
throw;
}
A single SaveChanges is already transactional; explicit transactions are needed when you combine several saves or raw SQL into one unit.
Most LINQ operators such as Where and Select do not run when you write them; they build a query that executes only when you enumerate it with foreach, ToList, Count or First. This means the query sees the latest data at enumeration time and can be composed step by step. The catch is that enumerating the same query twice runs it twice, which can mean two database calls. Call ToList to materialise once.
04
What are Span<T> and Memory<T> and why do they matter for performance?
Span<T> is a ref struct that represents a contiguous slice of memory, such as part of an array, a string or stack memory, without copying it. Slicing a span is free, which makes parsing much faster with zero allocations. Because it is stack-only, it cannot be stored in fields or used across await. Memory<T> is the heap-storable version for async code. ASP.NET Core and System.Text.Json use them heavily.
05
Why should we hire you as a .NET full stack developer?
I can contribute on both sides of a feature: I have built ASP.NET Core APIs with EF Core and SQL Server, and front ends in Angular and React, and deployed them myself. I write clean, tested code and I am comfortable reading logs and execution plans when things break. I learn quickly, ask questions early and take ownership, so you can give me a module and trust that it will be completed properly.
06
What is the difference between throw and throw ex inside a catch block?
throw rethrows the current exception and preserves the original stack trace, so logs show where the error really started. throw ex resets the stack trace to the catch block, hiding the real source. Always use throw when rethrowing. If you need more context, wrap it: throw new OrderException("Payment failed", ex), which keeps the original as InnerException. Also avoid catching Exception unless you log and rethrow.
07
What is the difference between controllers and Minimal APIs?
Controllers group actions into classes with attributes for routing, filters and model binding, which suits large APIs with many conventions. Minimal APIs map endpoints directly with app.MapGet and lambdas, with less ceremony and slightly better performance, ideal for microservices and small APIs. Since .NET 7 they support filters, route groups and OpenAPI, and .NET 10 adds built-in validation, so both are production-ready choices.
The Common Language Runtime is the execution engine of .NET. It loads compiled IL code, converts it to machine code with the JIT compiler, manages memory through the garbage collector, enforces type safety, handles exceptions and manages threads. Because every .NET language compiles to the same IL, C#, F# and VB.NET code can run on the same CLR and call each other.
09
What are nullable value types and nullable reference types?
Nullable value types like int? wrap a struct so it can hold null, with HasValue and Value properties. Nullable reference types, enabled by <Nullable>enable</Nullable>, are a compile-time feature: string means non-null and string? means may be null, and the compiler warns when you dereference a possible null. They do not change runtime behaviour but catch many NullReferenceException bugs before deployment.
Every HTTP request passes through a chain of middleware components configured in Program.cs. Each component can inspect or modify the request, call the next one, and then work on the response on the way back. Order matters: exception handling first, then HTTPS redirection, static files, routing, CORS, authentication, authorization and finally endpoints. For example, putting UseAuthorization before UseAuthentication means users never appear logged in.
11
What is SQL injection and how do you prevent it in a .NET application?
SQL injection happens when user input is concatenated into SQL text, letting attackers change the query, for example entering ' OR 1=1 -- in a login box. Prevent it by always using parameters: SqlCommand with SqlParameter, EF Core LINQ, FromSql with interpolation, or Dapper parameters. Also use least-privilege database accounts, validate input and never show raw database errors to users. Stored procedures help only if they also avoid dynamic SQL concatenation.
12
Write a query to find duplicate email addresses and delete the extra rows, keeping the lowest Id.
-- find duplicates
SELECT Email, COUNT(*) AS Cnt
FROM Users
GROUP BY Email
HAVING COUNT(*) > 1;
-- delete duplicates, keep lowest Id
WITH d AS (
SELECT Id, ROW_NUMBER() OVER (PARTITION BY Email ORDER BY Id) AS rn
FROM Users
)
DELETE FROM d WHERE rn > 1;
After cleanup, add a unique index on Email to stop duplicates returning.
13
Explain First, FirstOrDefault, Single and SingleOrDefault.
First returns the first match and throws if none exists. FirstOrDefault returns the default value, null for classes, if none exists. Single expects exactly one match and throws if there are zero or more than one. SingleOrDefault returns default for zero but still throws for more than one. Use Single when duplicates would indicate a data bug, such as lookup by unique PAN number; otherwise FirstOrDefault is cheaper.
14
What is the difference between compile-time and runtime polymorphism?
Compile-time, or static, polymorphism is resolved by the compiler, mainly through method overloading and operator overloading, and through generics. Runtime, or dynamic, polymorphism is resolved when the program runs, through virtual methods and interfaces: a Shape reference may call Circle.Area or Square.Area depending on the actual object. Runtime polymorphism is what makes plugin designs and dependency injection possible.
15
How do model binding and validation work in ASP.NET Core Web API?
Model binding maps request data into action parameters from the route, query string, headers or body, using [FromRoute], [FromQuery] and [FromBody]. Validation uses data annotations like [Required], [StringLength] and [Range] on DTOs. With [ApiController], invalid models automatically return 400 Bad Request with ProblemDetails listing the errors, so you do not need to check ModelState manually. FluentValidation is popular for complex rules.
public sealed class AppConfig
{
private static readonly Lazy<AppConfig> _instance =
new(() => new AppConfig());
public static AppConfig Instance => _instance.Value;
private AppConfig()
{
// load settings once
}
}
Lazy<T> is thread-safe by default and creates the object only on first access. The private constructor and sealed class prevent other instances. In ASP.NET Core, prefer AddSingleton.
17
What is ASP.NET Core and what are its main features?
ASP.NET Core is the open-source, cross-platform framework for building web APIs, MVC sites, Razor Pages, Blazor apps and real-time apps with SignalR on modern .NET. Key features are built-in dependency injection, a configurable middleware pipeline, the fast Kestrel web server, unified configuration and logging, and support for Docker and cloud hosting. It runs on Windows, Linux and macOS and consistently ranks among the fastest web frameworks.
public async IAsyncEnumerable<Order> GetOrdersAsync(
[EnumeratorCancellation] CancellationToken ct = default)
{
await foreach (var o in _db.Orders.AsNoTracking().AsAsyncEnumerable().WithCancellation(ct))
yield return o;
}
// consumer
await foreach (var order in service.GetOrdersAsync())
Console.WriteLine(order.Id);
Items are produced and consumed one at a time asynchronously. ASP.NET Core can stream an IAsyncEnumerable result as JSON without buffering the whole list.
19
What is the difference between DELETE, TRUNCATE and DROP?
DELETE removes rows one by one, supports WHERE, fires triggers and is fully logged, so it is slower on big tables. TRUNCATE removes all rows by deallocating pages, is minimally logged, resets identity values and cannot have WHERE; it fails if foreign keys reference the table. DROP removes the whole table including structure, indexes and permissions. In SQL Server, both DELETE and TRUNCATE can be rolled back inside a transaction.
20
What are components and standalone components in Angular?
A component is a TypeScript class with the @Component decorator, a template and styles, representing one piece of UI such as a product card. Earlier, every component had to be declared in an NgModule. Standalone components import their own dependencies directly through the imports array and need no module; since Angular 19 they are the default. This simplifies apps, enables easier lazy loading and is the recommended approach in 2026.
21
Write a switch expression using pattern matching to calculate shipping cost.
INNER JOIN returns rows that match in both tables. LEFT JOIN returns all rows from the left table plus matches from the right, with NULLs where there is no match. RIGHT JOIN is the mirror. FULL OUTER JOIN returns all rows from both sides. CROSS JOIN returns every combination. A self join joins a table to itself, such as employees to their managers. LEFT JOIN with WHERE right.Id IS NULL finds unmatched rows.
23
What is the difference between == and Equals() in C#?
For reference types, == by default checks reference equality, meaning both variables point to the same object, while Equals can be overridden to compare content. String overrides both, so == compares text. For value types, Equals compares field values. Records generate value-based equality automatically. When you override Equals, also override GetHashCode so objects behave correctly in dictionaries and hash sets.
24
What are useMemo and useCallback used for in React?
useMemo caches the result of an expensive calculation and recalculates only when its dependencies change, such as filtering 10,000 rows. useCallback caches a function reference so that a child wrapped in React.memo does not re-render just because a new function was created. Both are optimisations and add complexity, so use them where profiling shows a problem. The React Compiler, stable since late 2025, can apply much of this memoisation automatically.
Authorization filters run first and can block a request. Resource filters run before model binding, useful for caching. Action filters run before and after an action, for logging or validation. Exception filters handle errors thrown by actions. Result filters run around the result execution, for example to add headers. Filters apply globally, per controller or per action. Unlike middleware, they can access MVC details like action arguments.
EF Core is Microsoft's object-relational mapper for .NET. It maps C# classes to database tables, translates LINQ queries into SQL, tracks changes to loaded objects and saves them with SaveChanges. It supports SQL Server, PostgreSQL, MySQL, SQLite, Cosmos DB and more through providers. It removes most hand-written data access code, while still allowing raw SQL when needed. EF Core 10 ships with .NET 10.
27
What is the difference between code-first and database-first approaches?
In code-first, you write entity classes and a DbContext, and EF Core migrations create and evolve the database schema from code; it suits new projects and keeps schema in source control. In database-first, the database already exists and you scaffold entities with dotnet ef dbcontext scaffold. It suits legacy databases managed by a DBA team. Many teams scaffold once and then continue code-first.
28
What is the difference between var, dynamic and object?
var is implicitly typed: the compiler infers the real type at compile time, so it is fully type-safe. object is the base type of everything; you need casts to use specific members, and value types get boxed. dynamic skips compile-time checking and resolves members at runtime, so typos fail only when the code runs. Use var for readability, object rarely, and dynamic only for COM interop or truly dynamic data.
29
What is the difference between a clustered and a non-clustered index?
A clustered index defines the physical order of the table's data, so the leaf level is the data itself, and a table can have only one. A non-clustered index is a separate structure with key values and a pointer back to the row, and a table can have many. Range queries on the clustered key are fast. Non-clustered indexes speed up searches on other columns but add cost to inserts and updates.
30
Your security team objects to storing the JWT in localStorage in your Angular app. What are the options?
localStorage is readable by any JavaScript on the page, so an XSS bug can steal the token. A safer pattern is to keep the short-lived access token in memory and store the refresh token in an HttpOnly, Secure, SameSite cookie that scripts cannot read. Even better is the backend-for-frontend pattern, where ASP.NET Core holds tokens server-side and the browser uses a session cookie. Add CSRF protection when using cookies.
Tips to crack the EPAM Systems .NET Full Stack interview
Revise core concepts in Java, Python or JavaScript deeply, as EPAM interviews often test language fundamentals in detail.
Prepare test automation framework design questions if applying for QA roles, including page object model and CI integration.
Read about EPAM's engineering-first identity and its learning platforms, which it highlights for career growth.
Keep a one-minute story ready for every project on your CV: problem, your part, tools, result.
Practise the hard questions on this page aloud; EPAM Systems interviewers usually ask follow-ups on your first answer.
Frequently asked questions
How many rounds are there in the EPAM Systems .NET Full Stack interview?
Candidates usually go through 4 stages: Online coding assessment; Technical interview; Technical or design round; Hiring manager round. The exact rounds change with the role, team, location and your experience, so confirm the process with the recruiter.
Which topics should I prepare for the EPAM Systems .NET Full Stack interview?
This practice set leans on C# Fundamentals (7), SQL Server and T-SQL (6), ASP.NET Core Web API (5), Angular and React Front End (4). Revise those first, then practise explaining one or two of your own projects end to end, because most EPAM Systems interviewers ask you to walk through real work.
Are these the exact questions asked at EPAM Systems?
No. These are curated practice questions that match the skills and difficulty usually tested in it services interviews like EPAM Systems's. They are not a leaked or verified list of past questions.
Where does EPAM Systems hire .NET Full Stack professionals in India?
EPAM Systems has large teams in Hyderabad, Bengaluru, Pune, Chennai, Gurugram. Openings and locations change often, so check the EPAM Systems careers page and filter by city and experience.