Preventing overrides with final in Swift - Mini Project: Build & Apply

Preventing Overrides with final in Swift

📖 Scenario: Imagine you are creating a simple app to manage vehicles. You want to make sure that certain behaviors of your vehicle classes cannot be changed by mistake in subclasses.

🎯 Goal: You will create a base class with a method that cannot be overridden by subclasses using the final keyword. This helps keep your code safe and predictable.

📋 What You'll Learn

Create a class called Vehicle with a method startEngine() that prints a message.

Add the final keyword to the startEngine() method to prevent overriding.

Create a subclass called Car that inherits from Vehicle.

Try to override the startEngine() method in Car (this should cause an error if uncommented).

Create an instance of Car and call the startEngine() method.

Print the output to see the behavior.

💡 Why This Matters

🌍 Real World

In real apps, you often want to protect core behaviors of your classes so they don't change unexpectedly when others extend your code.

💼 Career

Understanding <code>final</code> helps you write safer, more reliable Swift code, a skill valued in iOS and macOS development jobs.

1

Create the Vehicle class with a startEngine() method

Create a class called Vehicle with a method startEngine() that prints "Engine started".

Swift

# Create the Vehicle class with startEngine() method
# Your code here

Need a hint?

Use class Vehicle {} and define func startEngine() inside it.

2

Make startEngine() method final to prevent overrides

Add the final keyword before the func startEngine() method in the Vehicle class to prevent it from being overridden.

Swift

class Vehicle {
    // Make startEngine() final
    # Your code here
}

Need a hint?

Write final func startEngine() to stop subclasses from changing this method.

3

Create a Car subclass inheriting from Vehicle

Create a subclass called Car that inherits from Vehicle. Inside Car, add a commented-out attempt to override startEngine() method that prints "Car engine started".

Swift

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

// Create Car subclass here
# Your code here

Need a hint?

Use class Car: Vehicle {} and inside it write a commented override of startEngine().

4

Create a Car instance and call startEngine()

Create an instance called myCar of the Car class and call the startEngine() method on it. Print the output.

Swift

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

class Car: Vehicle {
    // This override is not allowed because startEngine() is final
    // override func startEngine() {
    //     print("Car engine started")
    // }
}

// Create myCar instance and call startEngine()
# Your code here

Need a hint?

Write let myCar = Car() and then myCar.startEngine().