In C#, what is the primary purpose of using an interface?

The correct answer is B: To define a contract that classes must implement. Interfaces in C# define a set of method and property declarations that implementing classes must provide, establishing a contract without implementation details.

Consider a BankAccount class with private balance field. How should external classes access this field safely?

The correct answer is B: Use public properties with get/set accessors. Properties with accessors (get/set) follow encapsulation principles, allowing controlled access while maintaining data validation logic within the property.

Which of the following statements about virtual methods in C# is TRUE?

The correct answer is B: Virtual methods allow derived classes to override the base implementation. Virtual methods are designed to be overridden by derived classes, enabling polymorphic behavior and runtime method resolution.

In C#, what is the primary purpose of the 'using' statement?

The correct answer is B: To ensure proper resource disposal and implement IDisposable. The 'using' statement ensures that Dispose() is called on objects implementing IDisposable, preventing resource leaks. Importing namespaces is a different use of 'using'.

In an inventory management system, a Product class has a Price property. Which approach best ensures price cannot be negative?

The correct answer is B: Use private backing field with property validation in setter. Properties with private backing fields allow validation in setters, ensuring data integrity by preventing invalid values like negative prices.

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OOP in C#

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25 Q 4 Topics Take Mock Test

Difficulty: All Easy Medium Hard 11–20 of 25

Topics in C# Programming

All Basics & Syntax 100 OOP in C# 100 Collections 71 ASP.NET Basics 19

Q.11 Hard OOP in C#

What is covariance in C# generics and interfaces?

A Same type variance for all generic parameters

B Allowing derived types where base types are expected in return types

C Preventing type variance entirely

D Using 'in' keyword for contravariance only

Correct Answer: B. Allowing derived types where base types are expected in return types

EXPLANATION

Covariance (using 'out' keyword) allows a more derived type to be returned where a base type is expected, improving type safety and flexibility.

Test

Q.12 Hard OOP in C#

In C#, when implementing IDisposable pattern, what should a derived class do if the base class also implements it?

A Ignore the base implementation

B Call base.Dispose() within its Dispose() override

C Reimplement IDisposable completely

D Use only static Dispose methods

Correct Answer: B. Call base.Dispose() within its Dispose() override

EXPLANATION

Derived classes must call base.Dispose() to ensure proper cleanup of base class resources, following the disposable pattern correctly.

Test

Q.13 Hard OOP in C#

A developer needs to ensure that a method in a derived class cannot be overridden further. Which keyword should be used?

A virtual sealed

B sealed override

C abstract sealed

D override private

Correct Answer: B. sealed override

EXPLANATION

'sealed override' prevents further overriding of an already overridden virtual method in derived-from-derived classes.

Test

Q.14 Hard OOP in C#

In C# 10+, what is the purpose of the 'file-scoped type' modifier?

A To restrict type visibility to the current file only

B To improve code execution speed

C To enable file compression

D To manage file permissions

Correct Answer: A. To restrict type visibility to the current file only

EXPLANATION

The 'file' access modifier (C# 11+) restricts type visibility to the file it's declared in, improving encapsulation at the file level.

Test

Q.15 Hard OOP in C#

Consider a scenario where class C inherits from B, and B inherits from A. If all three have a method Display(), what does calling Display() on C object invoke?

A A's Display()

B B's Display()

C C's Display() if overridden, otherwise B's

D All three methods sequentially

Correct Answer: C. C's Display() if overridden, otherwise B's

EXPLANATION

Due to method overriding and polymorphism, C's Display() executes if overridden. Otherwise, the most derived available implementation in the inheritance chain executes.

Test

Q.16 Hard OOP in C#

A company develops a payment system using multiple payment methods (Credit Card, UPI, Wallet). Which OOP principle best applies here?

A Encapsulation only

B Polymorphism through interface implementation

C Inheritance only

D Abstraction only

Correct Answer: B. Polymorphism through interface implementation

EXPLANATION

Creating an IPayment interface with different payment classes implementing it demonstrates polymorphism, allowing the system to handle various payment methods uniformly.

Test

Q.17 Hard OOP in C#

What is the correct way to implement the Dispose pattern in C# for resource cleanup?

A Implement IDisposable with Dispose method and destructor

B Only implement a destructor

C Only implement the IDisposable interface

D Use only finalizers without IDisposable

Correct Answer: A. Implement IDisposable with Dispose method and destructor

EXPLANATION

The proper Dispose pattern implements IDisposable and uses a finalizer/destructor as a safety net, following the recommended pattern in C#.

Test

Q.18 Hard OOP in C#

In C# 12, what feature allows creating parameterless struct constructors with field initializers?

A Struct initialization expressions

B Field initializers in structs

C Explicit struct constructors

D Default struct methods

Correct Answer: B. Field initializers in structs

EXPLANATION

C# 12 allows field initializers directly in struct declarations, enabling parameterless constructors with initialized default values.

Test

Q.19 Hard OOP in C#

Which feature in C# 8+ allows you to provide default implementation in an interface?

A Virtual methods

B Default interface implementations

C Abstract methods

D Static constructors

Correct Answer: B. Default interface implementations

EXPLANATION

C# 8 introduced default interface implementations, allowing interfaces to have method bodies that implementing classes can inherit or override.

Test

Q.20 Hard OOP in C#

In C# 10, what does the 'file' access modifier allow?

A Access members across different files in the same project

B Restricts type visibility to the current file only

C Allows file-level access from external assemblies

D Enables file streaming operations for the type

Correct Answer: B. Restricts type visibility to the current file only

EXPLANATION

The 'file' scoped type modifier (C# 11) restricts a type to be visible only within the file it's declared in, preventing accidental public API expansion.

Test

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