Enum with when exhaustive check in Kotlin - Mini Project: Build & Apply

Enum with when exhaustive check

📖 Scenario: You are building a simple traffic light controller. The traffic light can be RED, YELLOW, or GREEN.You want to write code that reacts to each light color and prints the correct action for drivers.

🎯 Goal: Create an enum class for the traffic light colors, then use a when expression with exhaustive checking to print the correct action for each color.

📋 What You'll Learn

Create an enum class called TrafficLight with values RED, YELLOW, and GREEN

Create a variable called currentLight and set it to TrafficLight.RED

Use a when expression with variable currentLight to print the correct action for each color

Ensure the when expression is exhaustive (no else branch)

Print the action string exactly as specified

💡 Why This Matters

🌍 Real World

Traffic lights are common in real life and controlling their behavior in software helps understand state management.

💼 Career

Enums and exhaustive when expressions are widely used in Kotlin development for clear and safe handling of fixed sets of options.

1

Create the enum class

Create an enum class called TrafficLight with these exact values: RED, YELLOW, and GREEN.

Kotlin

# Your code here

Need a hint?

An enum class groups related constants. Use enum class TrafficLight { RED, YELLOW, GREEN }.

2

Create the currentLight variable

Create a variable called currentLight and set it to TrafficLight.RED.

Kotlin

enum class TrafficLight {
    RED, YELLOW, GREEN
}

# Your code here

Need a hint?

Use val currentLight = TrafficLight.RED to set the current light.

3

Write the when expression

Write a when expression using the variable currentLight to assign a variable action a string describing what drivers should do for each light: "Stop" for RED, "Get Ready" for YELLOW, and "Go" for GREEN. Do not use an else branch.

Kotlin

enum class TrafficLight {
    RED, YELLOW, GREEN
}

val currentLight = TrafficLight.RED

# Your code here

Need a hint?

Use val action = when (currentLight) { TrafficLight.RED -> "Stop" ... } without an else branch.

4

Print the action

Write a print statement to display the value of the variable action.

Kotlin

enum class TrafficLight {
    RED, YELLOW, GREEN
}

val currentLight = TrafficLight.RED

val action = when (currentLight) {
    TrafficLight.RED -> "Stop"
    TrafficLight.YELLOW -> "Get Ready"
    TrafficLight.GREEN -> "Go"
}

# Your code here

Need a hint?

Use println(action) to show the action.