Objective C Interview Questions

What is Objective-C and its importance in iOS development?

Objective-C is a programming language used to develop software for Apple's iOS and macOS operating systems. It is important in iOS development because it allows developers to create robust and efficient applications that can take full advantage of the features and capabilities offered by Apple's devices.

Explain the difference between a class and an object in Objective-C.

A class in Objective-C is a blueprint or template that defines the properties and behaviors of an object. An object is an instance of a class, meaning it is created based on the blueprint defined by the class. Objects have specific values for their properties and can perform actions as defined by the class.

What is message passing in Objective-C?

Message passing in Objective-C refers to the mechanism by which objects communicate with each other by sending and receiving messages. Objects can send messages to other objects to request some action or information, and the receiving object can respond accordingly. It is a key feature of the Objective-C language.

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What is a selector in Objective-C?

In Objective-C, a selector is the name that identifies a method. It is essentially a way to refer to a method by using its name. Selectors are often used in message passing between objects and allow for dynamic method invocation at runtime.

What is the use of @synthesize in Objective-C?

@synthesize in Objective-C is used to automatically generate getter and setter methods for declared properties. It is used to bind the property to an instance variable, reducing the need for manual implementation of accessors. This simplifies the code and enforces encapsulation in object-oriented programming.

What is memory management in Objective-C and how is it implemented?

Memory management in Objective-C involves allocating and releasing memory to prevent memory leaks or accessing deallocated memory. This is implemented by using reference counting with retain, release, and autorelease methods, as well as using Automatic Reference Counting (ARC) for managing memory automatically.

Explain the concept of Categories in Objective-C.

Categories in Objective-C allow you to add additional methods to existing classes without subclassing them. This provides a way to extend the functionality of a class without modifying its original implementation, making it useful for organizing and reusing code in a modular manner.

What is the purpose of protocols in Objective-C?

Protocols in Objective-C are used to declare methods that a class can choose to implement. They serve as a set of guidelines for what methods should be implemented by a class that adopts the protocol, promoting code reusability, modularity, and maintaining a clean separation of concerns.

What is ARC (Automatic Reference Counting) in Objective-C?

ARC (Automatic Reference Counting) is a memory management feature in Objective-C that automatically manages memory by keeping track of an object's references. It ensures that objects are deallocated from memory when they are no longer in use, reducing the possibility of memory leaks and improving performance.

How can you create an instance of a class in Objective-C?

To create an instance of a class in Objective-C, you can use the following code: ClassName *instanceName = [[ClassName alloc] init]; This code snippet initializes an instance of the class "ClassName" and stores it in the variable "instanceName" for further use.

What is a block in Objective-C?

A block in Objective-C is a piece of code that can be defined independently and passed around as an object. It is similar to a function or lambda expression in other programming languages. Blocks are commonly used for callbacks, asynchronous operations, and for encapsulating units of work.

Explain the difference between delegate and notification in Objective-C.

In Objective-C, a delegate is used for one-to-one communication between objects, where one object acts on behalf of another. Notifications, on the other hand, are a way for objects to broadcast information to multiple observers. Delegates have a specific receiver, while notifications are broadcasted to anyone interested.

What is the use of the keyword 'self' in Objective-C?

In Objective-C, the keyword 'self' is used to refer to the current instance of a class. It is commonly used to access instance variables and methods within the same class. This keyword is crucial for maintaining encapsulation and for distinguishing instance variables from local variables.

How can you handle exceptions in Objective-C?

In Objective-C, exceptions can be handled using the @try, @catch, and @finally blocks. Inside the @try block, the code that might throw an exception is written, and any potential exceptions are caught and handled in the @catch block. The @finally block is used to clean up resources.

What is the difference between assigning and retaining in Objective-C?

In Objective-C, assigning a value to an object pointer simply sets a reference to the object without changing its memory management. Retaining, on the other hand, increases the object's retain count, ensuring it is not deallocated until explicitly released. Retaining helps prevent memory leaks in the application.

Explain the concept of Key-Value Observing (KVO) in Objective-C.

Key-Value Observing (KVO) in Objective-C allows objects to observe changes to specified properties of another object. It enables one object to register itself with another object to receive notifications when the value of a specific property changes, without having to repeatedly check the value manually.

What are the different data types in Objective-C?

In Objective-C, the different data types include: 1. Primitive data types (such as int, float, double, char) 2. Objects (such as NSString, NSArray, NSDictionary) 3. Pointers (used to store memory addresses) 4. Structs (used to define custom data types) 5. Enums (used to define a set of named integer constants)

How can you define properties in Objective-C?

In Objective-C, properties can be defined using the `@property` keyword followed by the data type and property name in the interface file (.h), and then synthesized using the `@synthesize` keyword in the implementation file (.m) to create the getter and setter methods for the property.

Explain the difference between NSArray and NSMutableArray in Objective-C.

In Objective-C, NSArray is an immutable collection class that cannot be modified after creation, meaning its contents cannot be added, removed, or altered. In contrast, NSMutableArray is a mutable collection class that allows for dynamic modifications like adding, removing, or replacing objects within the array.

What is a singleton class in Objective-C and how can it be implemented?

A singleton class in Objective-C is a class that is designed to have only one instance throughout the application. It is typically implemented by creating a static method that returns a shared instance of the class, ensuring that only one instance is created and shared globally within the application.

What is Objective-C and its importance in iOS development?

Objective-C is a programming language used to develop software for Apple's iOS and macOS operating systems. It is important in iOS development because it allows developers to create robust and efficient applications that can take full advantage of the features and capabilities offered by Apple's devices.

Objective-C is a programming language that is a superset of the C programming language and is primarily used for developing software for Apple's macOS and iOS operating systems. It was introduced by NeXT in the late 1980s and later adopted by Apple. Objective-C is known for its dynamic runtime that allows for dynamic method resolution and object messaging.

In the context of iOS development, Objective-C has played a crucial role as the primary language for developing applications for Apple's mobile devices. It was the main programming language used for iOS development before the introduction of Swift. Objective-C remains relevant even today, with many legacy iOS applications still using it, and it is essential for developers who need to maintain or update older iOS codebases.

Objective-C is important in iOS development for several reasons:

  • Compatibility: Objective-C code can coexist with Swift code in the same project, allowing developers to leverage existing Objective-C libraries and frameworks while transitioning to Swift gradually.
  • Foundation Framework: Many core iOS frameworks, like Foundation and UIKit, are written in Objective-C. Understanding Objective-C is crucial for interfacing with these frameworks efficiently.
  • Legacy Codebase Maintenance: Many existing iOS applications are written in Objective-C. Developers need to be proficient in Objective-C to maintain, refactor, or update these legacy codebases.

Here is a simple example of Objective-C code for declaring a class and a method:

#import <Foundation/Foundation.h>

// Define a custom class in Objective-C
@interface MyClass: NSObject

// Declare a method in the class
- (void)printMessage;


@implementation MyClass

// Implement the method to print a message
- (void)printMessage {
    NSLog(@"Hello, Objective-C!");


int main() {
    // Create an instance of MyClass
    MyClass *myObject = [[MyClass alloc] init];
    // Call the method to print a message
    [myObject printMessage];
    return 0;

Objective-C has been a foundational language for iOS development and understanding it is still relevant for developers working on iOS applications. While Swift has become the preferred language for new iOS projects, Objective-C proficiency remains valuable for iOS developers.