Overriding methods and properties in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of overridden method call

What is the output of this Swift code when calling dog.makeSound()?

Swift

class Animal {
    func makeSound() {
        print("Some generic sound")
    }
}

class Dog: Animal {
    override func makeSound() {
        print("Bark")
    }
}

let dog = Dog()
dog.makeSound()

A Some generic sound

B Bark

C Compilation error due to missing override keyword

D Runtime error

💡 Hint

Remember that the override keyword allows a subclass to provide its own implementation of a method.

The Dog class overrides the makeSound() method of Animal. When calling dog.makeSound(), the overridden method in Dog runs, printing "Bark".

❓ Predict Output

intermediate

Output of overridden computed property

What will be printed when accessing circle.description in this Swift code?

Swift

class Shape {
    var description: String {
        return "A shape"
    }
}

class Circle: Shape {
    override var description: String {
        return "A circle"
    }
}

let circle = Circle()
print(circle.description)

A A shape

B Runtime error

C Compilation error: cannot override stored property

D A circle

💡 Hint

Check how computed properties can be overridden with override var.

The Circle class overrides the computed property description from Shape. Accessing circle.description calls the overridden property, printing "A circle".

🔧 Debug

advanced

Identify the error in method overriding

Which option correctly explains the error in this Swift code?

Swift

class Vehicle {
    func startEngine() {
        print("Engine started")
    }
}

class Car: Vehicle {
    func startEngine() {
        print("Car engine started")
    }
}

A No error, code runs and prints "Car engine started"

B Runtime error due to method ambiguity

C Compilation error: missing 'override' keyword before 'startEngine()' in Car

D Compilation error: cannot override a method without 'final' keyword

💡 Hint

In Swift, overriding a method requires the override keyword.

The Car class tries to override startEngine() but misses the override keyword, causing a compilation error.

❓ Predict Output

advanced

Output of property observer in overridden property

What is the output when setting mySquare.sideLength = 10 in this Swift code?

Swift

class Square {
    var sideLength: Int = 0 {
        willSet {
            print("Square will set sideLength to \(newValue)")
        }
    }
}

class ColoredSquare: Square {
    override var sideLength: Int {
        get {
            super.sideLength
        }
        set {
            print("ColoredSquare will set sideLength to \(newValue)")
            super.sideLength = newValue
        }
    }
}

let mySquare = ColoredSquare()
mySquare.sideLength = 10

A ColoredSquare will set sideLength to 10

B Square will set sideLength to 10

C Both "Square will set sideLength to 10" and "ColoredSquare will set sideLength to 10"

D No output

💡 Hint

Overridden property observers replace the superclass observers.

The ColoredSquare overrides the property observer willSet. Only the overridden observer runs, printing "ColoredSquare will set sideLength to 10".

🧠 Conceptual

expert

Behavior of overriding a property with different types

Consider this Swift code. What error will occur and why?

Swift

class Parent {
    var value: Int {
        return 5
    }
}

class Child: Parent {
    override var value: String {
        return "Five"
    }
}

A Compilation error: Cannot override property with a different type

B Runtime error: Type mismatch when accessing value

C No error, Child's value returns "Five" as String

D Compilation error: Missing 'override' keyword

💡 Hint

Overriding properties must keep the same type in Swift.

Swift requires the overridden property to have the same type as the original. Changing from Int to String causes a compilation error.