Overriding methods and properties in Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does it mean to override a method in Swift?

Overriding a method means providing a new version of a method in a subclass that replaces the version defined in its superclass.

beginner

How do you indicate that a method or property is being overridden in Swift?

You use the override keyword before the method or property declaration in the subclass.

intermediate

Can you override a property in Swift? If yes, what kinds of properties can be overridden?

Yes, you can override computed properties and property observers, but not stored properties directly.

beginner

What happens if you try to override a method without using the override keyword?

Swift will give a compile-time error because it requires explicit use of override to avoid accidental overrides.

intermediate

Explain how to call the superclass version of an overridden method in Swift.

Inside the overriding method, you call super.methodName() to run the original method from the superclass.

Which keyword is required to override a method in Swift?

A override

B super

C extends

D func

The override keyword tells Swift you are replacing a method or property from the superclass.

What will happen if you override a method but forget to write the override keyword?

A Swift gives a compile-time error

B The program runs normally

C The superclass method is called instead

D The method is ignored

Swift requires the override keyword to prevent accidental overrides, so it gives an error if missing.

How do you call the original method from the superclass inside an overridden method?

A parent.methodName()

B self.methodName()

C super.methodName()

D base.methodName()

Using super.methodName() calls the superclass version of the method.

Which of these can be overridden in Swift?

A Stored properties

B Local variables

C Constants

D Computed properties

You can override computed properties and property observers, but not stored properties directly.

Why is overriding useful in programming?

A To reuse code without changes

B To change or extend behavior of inherited methods

C To create new classes

D To delete superclass methods

Overriding lets subclasses change or add to the behavior of methods they inherit.

Describe how to override a method in Swift and how to call the original method from the superclass.

Think about the keywords and syntax needed to replace and extend a method.

Explain what kinds of properties can be overridden in Swift and why stored properties are treated differently.

Consider how properties store or calculate values.

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