Swift Classes Interview Questions (Beginner to Advanced)

Beginner Level

What is a class in Swift?
Answer
- In Swift, A class is a blueprint or template used to create objects, which are instances of that class. It allows for defining properties (data) and methods (functions) that can perform actions using those properties. Classes are reference types, meaning objects created from the same class share the same memory reference.
```
 class Person {
   var name: String
   var age: Int
 
     init(name: String, age: Int) {
         self.name = name
         self.age = age
     }
 
     func greet() {
         print("Hello, my name is \(name).")
     }
 }
```

How does a class differ from a structure?
Answer

Class is a reference type, while Struct is a value type.
When you assign or pass a class instance, you are passing a reference to the same memory, but with a struct, you are passing a copy.
Classes support inheritance, while structs do not.
Classes can be deinitialized, while structs cannot.

struct Car {
    var model: String
}
    
class Vehicle {
    var model: String

    init(model: String) {
        self.model = model
    }
}

var car1 = Car(model: "Sedan")
var car2 = car1
car2.model = "SUV"
print(car1.model)  // Output: Sedan

var vehicle1 = Vehicle(model: "Sedan")
var vehicle2 = vehicle1
vehicle2.model = "SUV"
print(vehicle1.model)  // Output: SUV

In the above example, the struct copy doesn’t affect the original, but the class reference does.

How do you create an instance of a class in Swift?
Answer To create an instance of a class, you initialize the class using the init method.
```
let person = Person(name: "Priyank", age: 30)
person.greet() // Output: Hello, my name is Priyank.
```

What are properties in a class?
Answer Properties in a class are variables or constants that hold data for the class. There are two types:

Stored Properties: Store actual values.
Computed Properties: Calculate values dynamically.

 class Circle {
     var radius: Double
     var area: Double {
         return 3.14 * radius * radius
     }
 
     init(radius: Double) {
         self.radius = radius
     }
 }

In above example, radius is a stored property and area is a computed property.

How do you declare methods inside a class?
Answer Methods in a class are declared like functions inside the class scope. They can access the class's properties and other methods.

class Animal {
    var name: String

    init(name: String) {
        self.name = name
    }

    func sound() {
        print("\(name) makes a sound.")
    }
}

What is a designated initializer?
Answer A designated initializer is the primary initializer for a class that fully initializes all properties and calls the superclass's initializer (if applicable). It’s the main entry point for creating instances of the class.
```
class Rectangle {
    var width: Double
    var height: Double

    // Designated Initializer
    init(width: Double, height: Double) {
        self.width = width
        self.height = height
    }
}
```
What is the difference between a class and an object?
Answer
- A class is a blueprint that defines the properties and methods.
- An object (or instance) is an actual realization of the class.
You can think of a class as the definition of a house, and an object as the actual house built from that definition.
```
class Dog {
    var breed: String

    init(breed: String) {
        self.breed = breed
    }
}

let dog = Dog(breed: "Labrador")
```

In above example, Dog is the class, and dog is the object created from that class.

How do you define static properties in a class?
Answer A static property in a class is shared by all instances of the class. It's defined using the static keyword and is associated with the class itself rather than any instance.

class Planet {
    static var planetCount = 0
    var name: String

    init(name: String) {
        self.name = name
        Planet.planetCount += 1
    }
}

let earth = Planet(name: "Earth")
let mars = Planet(name: "Mars")

print(Planet.planetCount) // Output: 2

What is inheritance in Swift?
Answer Inheritance allows one class to inherit properties, methods, and other characteristics from another class. In Swift, this is done using a colon (:) after the class name.

class Vehicle {
     var speed: Int = 0
     func drive() {
         print("Driving at \(speed) mph")
     }
 }

 class Car: Vehicle {
     var model: String
 
     init(model: String) {
         self.model = model
         super.init()  // Calls the superclass initializer
     }
 
     override func drive() {
         print("Car \(model) driving at \(speed) mph")
     }
 }

 let myCar = Car(model: "Tesla")
 myCar.speed = 60
 myCar.drive()  // Output: Car Tesla driving at 60 mph

In this example, Car inherits from Vehicle.

Can a class have default property values?
Answer Yes, a class can have default property values. This means that if a property is not explicitly initialized, it will take the default value.
```
class User {
    var name: String = "Guest"
    var age: Int = 18
}

let newUser = User()
print(newUser.name)  // Output: Guest
```

Intermediate Level

What is method overriding? Provide an example.
Answer coming soon...
Explain how subclassing works in Swift.
Answer coming soon...
What is a convenience initializer?
Answer coming soon...
What is the role of super.init() in subclassing?
Answer coming soon...
How does Swift handle access control with classes (e.g., public, private)?
Answer coming soon...
What are computed properties in a class?
Answer coming soon...
Explain how optional chaining works with class properties.
Answer coming soon...
What are class methods in Swift?
Answer coming soon...
Explain the concept of class inheritance.
Answer coming soon...
What are deinitializers, and when are they called?
Answer coming soon...

Advanced Level

What is the difference between a reference type and a value type?
Answer coming soon...
How do reference counting and memory management work with classes?
Answer coming soon...
How do you avoid retain cycles in classes?
Answer coming soon...
Explain method dispatch in Swift.
Answer coming soon...
Can a class conform to a protocol? Provide an example.
Answer coming soon...
What is polymorphism, and how does it work with classes?
Answer coming soon...
How does the required keyword affect class initializers?
Answer coming soon...
How do you create abstract classes in Swift?
Answer coming soon...
Can you explain how class clusters are used in Swift?
Answer coming soon...
How does Swift handle dynamic method dispatching?
Answer coming soon...

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Swift Classes Interview Questions (Beginner to Advanced)

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