Top Objective-C Interview Questions and Answers

Here are top Objective-C interview questions,

1. What is Objective-C?

Objective-C is a programming language used for developing iOS and macOS applications. It is an extension of the C programming language with added object-oriented capabilities.

 

2. What is the difference between Object-Oriented Programming (OOP) and Procedural Programming?

OOP is a programming paradigm that focuses on objects and classes, emphasizing data encapsulation, inheritance, and polymorphism. Procedural programming, on the other hand, is centered around procedures or functions.

 

3. What is a class in Objective-C?

A class is a blueprint or template that defines the structure and behavior of objects in Objective-C.

 

4. How do you create an instance of a class in Objective-C?

To create an instance of a class, you use the `alloc` and `init` methods together. For example:

```objective-c

MyClass *myObject = [[MyClass alloc] init];

```

 

5. What is a property in Objective-C?

A property defines the attributes of an object's instance variables. It provides a way to encapsulate data and allows access through getter and setter methods.

 

6. Explain the difference between `nonatomic` and `atomic` in Objective-C.

- `nonatomic`: It specifies that the generated accessor methods for the property are not thread-safe, which can improve performance but may cause issues in multi-threaded environments.

- `atomic`: It specifies that the generated accessor methods are thread-safe, ensuring data integrity but potentially impacting performance.

 

7. What are protocols in Objective-C?

Protocols define a set of methods that a class can implement, acting as a contract to ensure that a class adheres to certain behavior.

 

8. Explain the concept of memory management in Objective-C.

Objective-C uses Automatic Reference Counting (ARC) to manage memory. ARC automatically keeps track of object references and deallocates objects when they are no longer in use.

 

9. What is the delegate pattern in Objective-C?

The delegate pattern is a design pattern used to establish communication between objects. One object delegates certain tasks or responsibilities to another object.

 

10. What is a block in Objective-C?

A block is a language-level feature in Objective-C that encapsulates code segments, similar to closures or lambda functions in other programming languages.

 

11. Explain the difference between `copy`, `strong`, and `weak` in property attributes.

- `copy`: Creates a new, independent copy of the object when setting the property (usually used for NSString and other mutable classes).

- `strong`: Creates a strong reference to the object, increasing its retain count.

- `weak`: Creates a weak reference to the object, which does not increase its retain count (used to prevent retain cycles).

 

12. What is a selector in Objective-C?

A selector is a way to represent the name of a method. It is commonly used to invoke methods on objects at runtime.

 

13. Explain the difference between `retain`, `assign`, and `strong` in MRR (Manual Reference Counting).

- `retain`: Increases the retain count of an object.

- `assign`: Directly assigns a reference to the property, without increasing the retain count.

- `strong`: Similar to `retain` but used under Automatic Reference Counting (ARC).

 

14. What is KVC (Key-Value Coding) in Objective-C?

KVC is a mechanism to access an object's properties using strings as keys, allowing for dynamic property access.

 

15. How do you handle exceptions in Objective-C?

Objective-C uses the `@try`, `@catch`, and `@finally` blocks to handle exceptions similar to traditional exception handling in other programming languages.

 

16. What is the difference between categories and extensions in Objective-C?

- Categories: Allow you to add new methods to existing classes without subclassing them. Useful for extending frameworks or library classes.

- Extensions: Used to declare additional private methods or properties within a class's implementation file.

 

17. Explain the `self` keyword in Objective-C.

`self` refers to the current instance of the class. It is used to access the instance variables or call methods of the current object.

 

18. What is the role of the `@synthesize` directive?

In previous versions of Objective-C, `@synthesize` was used to generate getter and setter methods for properties. However, with modern Objective-C and ARC, it is no longer required, as properties are automatically synthesized.

 

19. What are the `getter` and `setter` keywords used for in property declaration?

The `getter` and `setter` keywords allow you to specify custom names for the getter and setter methods of a property.

 

20. Explain the difference between shallow copy and deep copy in Objective-C.

- Shallow copy: Copies only the references of objects, not the objects themselves. Changes in the copied objects will affect the original objects.

- Deep copy: Creates independent copies of objects, including the objects they contain. Changes in the copied objects will not affect the original objects.

 

Above are few top Objective-C interview questions. Remember to prepare and expand on these answers.

Good luck with your interview!  👍