Overriding methods and properties in Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to override the method describe() in the subclass.

Swift

class Animal {
    func describe() {
        print("I am an animal.")
    }
}

class Dog: Animal {
    override func [1]() {
        print("I am a dog.")
    }
}

Drag options to blanks, or click blank then click option'

Adescription

Bdescribe

CdescribeAnimal

DprintDescription

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different method name so the method is not actually overridden.

Forgetting the override keyword.

The method describe() is overridden by using the exact same method name with the override keyword.

2fill in blank

medium

Complete the code to override the computed property description in the subclass.

Swift

class Vehicle {
    var description: String {
        return "A vehicle"
    }
}

class Car: Vehicle {
    override var [1]: String {
        return "A car"
    }
}

Drag options to blanks, or click blank then click option'

Adescription

Bdesc

Cinfo

Ddetails

Attempts:

3 left

💡 Hint

Common Mistakes

Changing the property name so it does not override.

Not using the override keyword.

The property description is overridden by using the exact same property name with the override keyword.

3fill in blank

hard

Fix the error in the code by correctly overriding the method makeSound().

Swift

class Bird {
    func makeSound() {
        print("Chirp")
    }
}

class Parrot: Bird {
    override func [1]() {
        print("Squawk")
    }
}

Drag options to blanks, or click blank then click option'

AmakeSound

BmakeNoise

Csound

Dspeak

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different method name so it does not override.

Omitting the override keyword.

The method makeSound() is overridden by using the exact same method name with the override keyword.

4fill in blank

hard

Fill both blanks to override the property speed with a getter and setter.

Swift

class Machine {
    var speed: Int = 0
}

class Car: Machine {
    override var [1]: Int {
        get {
            return super.[2]
        }
        set {
            super.speed = newValue
        }
    }
}

Drag options to blanks, or click blank then click option'

Aspeed

Bvelocity

Dpower

Attempts:

3 left

💡 Hint

Common Mistakes

Using different property names in the override and super access.

Forgetting the override keyword.

The property name must be speed in both places to correctly override the property and access the superclass property.

5fill in blank

hard

Fill both blanks to override a method with parameters and call the superclass method inside.

Swift

class Printer {
    func printMessage(_ message: String) {
        print("Printer: \(message)")
    }
}

class ColorPrinter: Printer {
    override func [1](_ message: String) {
        print("ColorPrinter:")
        super.[2](message)
        print("Done printing.")
    }
}

Drag options to blanks, or click blank then click option'

AprintMessage

CprintMsg

Dprint

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different method name so it does not override.

Not calling the superclass method correctly.

The method name must be printMessage to override correctly and call the superclass method with super.printMessage(message).

Practice

1.

What keyword must you use in Swift to change a method from a parent class in a subclass?

easy

A. override

B. super

C. extend

D. inherit

Solution

1. Step 1: Understand method overriding in Swift

   Swift requires a special keyword to indicate a method is being changed in a subclass.

2. Step 2: Identify the correct keyword

   The keyword to override a method or property is override.

3. Final Answer:

   override -> Option A

4. Quick Check:

   Keyword to change parent method = override [OK]

Hint: Use 'override' before methods to change them in subclasses [OK]

Common Mistakes:

• Using 'super' instead of 'override'
• Forgetting the 'override' keyword
• Using 'extend' which is not a Swift keyword

2.

Which of the following is the correct syntax to override a method named greet() in Swift?

class Parent {
    func greet() {
        print("Hello")
    }
}

class Child: Parent {
    ??? func greet() {
        print("Hi")
    }
}

easy

A. override

B. super

C. func override

D. override func

Solution

1. Step 1: Recall Swift override syntax

   In Swift, the keyword override comes before the func keyword.

2. Step 2: Match the correct syntax

   The correct syntax is override func greet().

3. Final Answer:

   override func -> Option D

4. Quick Check:

   Keyword order is 'override func' [OK]

Hint: Write 'override' before 'func' to override methods [OK]

Common Mistakes:

• Writing 'func override' instead of 'override func'
• Using 'super' keyword instead of 'override'
• Omitting 'override' keyword entirely

3.

What will be the output of the following Swift code?

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

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

let pet: Animal = Dog()
pet.sound()

medium

A. Some sound

B. Bark

C. Compile error

D. Runtime error

Solution

1. Step 1: Understand method overriding and polymorphism

   Even though the variable type is Animal, the actual object is Dog, so overridden method runs.

2. Step 2: Identify which method is called

   The Dog's overridden sound() method prints "Bark".

3. Final Answer:

   Bark -> Option B

4. Quick Check:

   Overridden method runs on subclass instance [OK]

Hint: Overridden methods run on subclass instances even if typed as parent [OK]

Common Mistakes:

• Thinking parent method runs because variable type is Animal
• Expecting compile or runtime error
• Confusing method overriding with overloading

4.

Identify the error in this Swift code that tries to override a property:

class Vehicle {
    var speed: Int = 0
}

class Car: Vehicle {
    var speed: Int = 100
}

medium

A. Missing 'override' keyword before 'var speed' in subclass

B. Cannot override properties in Swift

C. Property types must differ when overriding

D. Superclass property must be 'let' to override

Solution

1. Step 1: Check property overriding rules

   To override a property in Swift, you must use the override keyword.

2. Step 2: Identify missing keyword

   The subclass property speed lacks the override keyword, causing an error.

3. Final Answer:

   Missing 'override' keyword before 'var speed' in subclass -> Option A

4. Quick Check:

   Override properties need 'override' keyword [OK]

Hint: Always add 'override' before properties you change in subclass [OK]

Common Mistakes:

• Forgetting 'override' keyword on properties
• Thinking properties cannot be overridden
• Changing property type when overriding

5.

Given this Swift code, what will be printed?

class Person {
    var description: String {
        return "Person"
    }
}

class Student: Person {
    override var description: String {
        return super.description + " - Student"
    }
}

let s = Student()
print(s.description)

hard

A. Person

B. Student

C. Person - Student

D. Compile error due to super usage

Solution

1. Step 1: Understand property overriding with super

   The subclass overrides description and calls super.description to get parent value.

2. Step 2: Combine parent and subclass strings

   The returned string is "Person" + " - Student" = "Person - Student".

3. Final Answer:

   Person - Student -> Option C

4. Quick Check:

   super.property adds parent value [OK]

Hint: Use 'super' to include parent property value when overriding [OK]

Common Mistakes:

• Expecting only 'Student' without parent text
• Thinking 'super' causes compile error
• Not using 'override' keyword on property