Objective-C Interview Questions and Answers for 2 years experience

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100 Objective-C Interview Questions & Answers

  1. What is Objective-C?

    • Answer: Objective-C is a general-purpose, object-oriented programming language that adds Smalltalk-style messaging to the C programming language. It's the primary programming language used for developing macOS and iOS applications.

  2. Explain the difference between `@interface` and `@implementation`

    • Answer: `@interface` declares the class's public interface – its properties and methods. `@implementation` provides the actual code for the methods declared in the interface.

  3. What are properties in Objective-C?

    • Answer: Properties are a convenient way to declare instance variables and access methods (getter and setter) for them. They simplify code and improve encapsulation.

  4. What are the different property attributes in Objective-C? (e.g., `nonatomic`, `strong`, `weak`, `copy`, `retain`)

    • Answer: `nonatomic`: Disables atomic access to the property (faster, but not thread-safe). `strong`: Creates a strong reference (object will not be deallocated as long as the property holds a reference). `weak`: Creates a weak reference (object can be deallocated without affecting the property). `copy`: Creates a copy of the object. `retain`: Increases the retain count of the object (less common now with ARC).

  5. Explain Automatic Reference Counting (ARC).

    • Answer: ARC is a memory management system that automatically handles object lifetimes. It reduces memory leaks and crashes by automatically releasing objects when they are no longer needed.

  6. What is a delegate?

    • Answer: A delegate is an object that acts on behalf of another object. It's a common design pattern used to handle events or notifications.

  7. What is a protocol?

    • Answer: A protocol defines a set of methods that a class can adopt (implement). It allows for loose coupling and polymorphism.

  8. Explain the difference between a class and a category.

    • Answer: A class defines a new data type, while a category adds methods to an existing class without subclassing. Categories are useful for extending functionality without modifying the original class.

  9. What is a singleton? How do you implement it in Objective-C?

    • Answer: A singleton is a class that guarantees only one instance of itself exists. It's typically implemented using a static variable to hold the instance and a class method to access it. Thread safety considerations are important in multithreaded environments.

  10. What is polymorphism?

    • Answer: Polymorphism allows objects of different classes to be treated as objects of a common type. It's a key feature of object-oriented programming.

  11. Explain inheritance in Objective-C.

    • Answer: Inheritance allows a class (subclass) to inherit properties and methods from another class (superclass). It promotes code reuse and establishes an "is-a" relationship.

  12. What is encapsulation?

    • Answer: Encapsulation bundles data (instance variables) and methods that operate on that data within a class, protecting the data from outside access and misuse.

  13. What is the difference between `self` and `super`?

    • Answer: `self` refers to the current instance of the class. `super` refers to the superclass of the current class, allowing you to call methods in the superclass.

  14. What is KVO (Key-Value Observing)?

    • Answer: KVO is a mechanism that allows objects to be notified of changes to the properties of other objects.

  15. What is KVC (Key-Value Coding)?

    • Answer: KVC is a mechanism that allows you to access and modify an object's properties using strings instead of direct method calls.

  16. Explain blocks in Objective-C.

    • Answer: Blocks are anonymous functions that can be passed around like objects. They are useful for callbacks and closures.

  17. What is Grand Central Dispatch (GCD)?

    • Answer: GCD is a low-level API for concurrent programming in iOS and macOS. It manages threads and allows for efficient parallel execution of tasks.

  18. What are NSOperation and NSOperationQueue?

    • Answer: `NSOperation` represents a unit of work, and `NSOperationQueue` manages a pool of threads to execute operations concurrently. It offers a higher-level abstraction over GCD.

  19. How do you handle memory management in Objective-C?

    • Answer: With ARC, memory management is largely automatic. However, understanding strong and weak references, and potential circular references is still crucial.

  20. What is a strong reference cycle? How do you break it?

    • Answer: A strong reference cycle occurs when two or more objects have strong references to each other, preventing them from being deallocated. Using `weak` references can break these cycles.

  21. Explain the difference between mutable and immutable objects.

    • Answer: Mutable objects can be changed after creation, while immutable objects cannot be modified after creation.

  22. What are some common Objective-C data structures? (e.g., NSArray, NSDictionary, NSSet)

    • Answer: `NSArray`: Ordered collection of objects. `NSDictionary`: Collection of key-value pairs. `NSSet`: Unordered collection of unique objects.

  23. How do you perform exception handling in Objective-C?

    • Answer: Objective-C uses `@try`, `@catch`, and `@finally` blocks for exception handling.

  24. What is the purpose of the `id` type?

    • Answer: `id` is a generic object pointer. It can point to any Objective-C object.

  25. Explain the difference between `nil` and `NULL`

    • Answer: `nil` is a null pointer for Objective-C objects. `NULL` is a null pointer for C pointers.

  26. What is a selector?

    • Answer: A selector is a type that represents a method. It's used in method calls and introspection.

  27. What are some common design patterns used in Objective-C development?

    • Answer: Singleton, Delegate, Observer, MVC (Model-View-Controller), Factory.

  28. How do you perform networking operations in Objective-C?

    • Answer: Using frameworks like NSURLSession or third-party libraries like AFNetworking.

  29. How do you handle asynchronous operations in Objective-C?

    • Answer: Using GCD, NSOperationQueue, or completion blocks.

  30. Explain how you would handle data persistence in Objective-C.

    • Answer: Using Core Data, SQLite, or NSUserDefaults depending on the complexity and data requirements.

  31. How do you debug Objective-C code?

    • Answer: Using Xcode's debugger, breakpoints, logging, and instruments.

  32. What are some common ways to handle errors in Objective-C?

    • Answer: Error objects, NSError, exception handling, and careful checking of return values.

  33. Explain your experience with using Core Data.

    • Answer: [Describe your experience with Core Data, including specific tasks, challenges, and solutions. Quantify your experience if possible.]

  34. Explain your experience with using Grand Central Dispatch (GCD).

    • Answer: [Describe your experience with GCD, including specific use cases, such as queues, dispatch groups, and barriers. Quantify your experience if possible.]

  35. How familiar are you with memory profiling tools?

    • Answer: [Describe your familiarity with Xcode's memory profiling tools and your experience using them to identify and resolve memory leaks. Mention specific tools if you have used them.]

  36. Describe your experience with working on a team using Git.

    • Answer: [Describe your experience with Git, including branching strategies, merging, pull requests, and resolving conflicts. Mention specific tools or workflows you've used.]

  37. How do you stay up-to-date with the latest technologies and trends in iOS development?

    • Answer: [Describe your methods for staying current, such as following blogs, attending conferences, reading Apple's documentation, participating in online communities, etc.]

  38. What are some of the challenges you've faced in Objective-C development, and how did you overcome them?

    • Answer: [Describe specific challenges you've faced, such as memory management issues, concurrency problems, or debugging complex code. Explain how you approached the problems and the solutions you implemented.]

  39. What are your preferred coding practices and why?

    • Answer: [Describe your coding practices, such as using descriptive variable names, commenting your code, following a consistent coding style, and writing unit tests. Explain why these practices are important to you.]

  40. Describe a time you had to debug a complex issue in Objective-C. What was your approach?

    • Answer: [Describe a specific instance where you had to debug a complex issue. Explain your systematic approach to troubleshooting, such as using logging, breakpoints, and stepping through the code. Highlight the problem-solving skills you utilized.]

  41. How do you handle deadlines and pressure in a fast-paced development environment?

    • Answer: [Describe your approach to managing time and stress, such as prioritizing tasks, breaking down large tasks into smaller ones, and seeking help when needed.]

  42. What are your strengths and weaknesses as an Objective-C developer?

    • Answer: [Be honest and provide specific examples. Focus on strengths relevant to the job description and frame weaknesses as areas for improvement.]

  43. Why are you interested in this position?

    • Answer: [Explain your interest in the company, the role, and the team. Show that you've done your research and that your skills and experience align with the company's needs.]

  44. Where do you see yourself in five years?

    • Answer: [Demonstrate ambition and a desire for growth within the company. Align your goals with the company's long-term vision.]

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