Class delegation with by keyword in Kotlin - Mini Project: Build & Apply

Class delegation with by keyword

📖 Scenario: Imagine you are building a simple app to manage different types of workers in a company. Some workers have special skills, but you want to reuse existing skill implementations without rewriting code.

🎯 Goal: You will create a Kotlin program that uses class delegation with the by keyword to share behavior between classes easily.

📋 What You'll Learn

Create an interface called Worker with a function work() that returns a String.

Create a class called BasicWorker that implements Worker and returns "Working hard" from work().

Create a class called Manager that delegates Worker behavior to a BasicWorker instance using the by keyword.

Print the result of calling work() on a Manager instance.

💡 Why This Matters

🌍 Real World

Class delegation helps reuse code and share behavior between classes without repeating code. It is useful in apps with many similar roles or behaviors.

💼 Career

Understanding delegation is important for Kotlin developers to write clean, maintainable code and use language features effectively in real projects.

1

Create the Worker interface and BasicWorker class

Create an interface called Worker with a function work() that returns a String. Then create a class called BasicWorker that implements Worker and its work() function returns the exact string "Working hard".

Kotlin

// Define interface Worker with function work() returning String
// Define class BasicWorker implementing Worker with work() returning "Working hard"
// Your code here

Need a hint?

Use interface to define Worker. Implement work() in BasicWorker to return the string exactly.

2

Create Manager class delegating Worker to BasicWorker

Create a class called Manager that implements Worker by delegating to a BasicWorker instance using the by keyword. Inside Manager, declare a primary constructor parameter called worker of type Worker and delegate Worker to it.

Kotlin

interface Worker {
    fun work(): String
}

class BasicWorker : Worker {
    override fun work(): String {
        return "Working hard"
    }
}

// Define class Manager that delegates Worker to a Worker instance using 'by'
// Your code here

Need a hint?

Use class Manager(private val worker: Worker) : Worker by worker to delegate all Worker functions to the worker instance.

3

Create a Manager instance delegating to BasicWorker

Create a variable called manager and assign it a new Manager instance that delegates to a new BasicWorker instance.

Kotlin

interface Worker {
    fun work(): String
}

class BasicWorker : Worker {
    override fun work(): String {
        return "Working hard"
    }
}

class Manager(private val worker: Worker) : Worker by worker

// Create a variable manager as Manager delegating to BasicWorker
// Your code here

Need a hint?

Use val manager = Manager(BasicWorker()) to create the instance.

4

Print the work result from Manager

Write a println statement to print the result of calling work() on the manager variable.

Kotlin

interface Worker {
    fun work(): String
}

class BasicWorker : Worker {
    override fun work(): String {
        return "Working hard"
    }
}

class Manager(private val worker: Worker) : Worker by worker

val manager = Manager(BasicWorker())

// Print the result of manager.work()
// Your code here

Need a hint?

Use println(manager.work()) to show the delegated work result.