Generic class declaration in Kotlin - Mini Project: Build & Apply

Generic class declaration

📖 Scenario: Imagine you want to create a box that can hold any type of item, like a box for toys, books, or fruits. Instead of making a new box for each type, you can make one generic box that works for all.

🎯 Goal: You will create a generic class called Box that can hold one item of any type. Then, you will create a box for an Int and a box for a String, and finally print the contents.

📋 What You'll Learn

Create a generic class called Box with one type parameter T

Add a property called item of type T to the class

Create a variable intBox of type Box<Int> holding the number 123

Create a variable stringBox of type Box<String> holding the text "Hello"

Print the contents of intBox and stringBox

💡 Why This Matters

🌍 Real World

Generic classes let you write flexible code that works with many data types without repeating yourself. For example, collections like lists and maps use generics.

💼 Career

Understanding generics is important for Kotlin developers to write reusable and type-safe code, which is a common requirement in professional software development.

1

Create the generic class

Create a generic class called Box with one type parameter T. Inside the class, add a property called item of type T. Use a primary constructor to set item.

Kotlin

# Your code here

Need a hint?

Use class Box<T>(val item: T) to declare the generic class.

2

Create an integer box

Create a variable called intBox of type Box<Int> and set it to hold the number 123.

Kotlin

class Box(val item: T)
# Your code here

Need a hint?

Write val intBox: Box<Int> = Box(123) to create the integer box.

3

Create a string box

Create a variable called stringBox of type Box<String> and set it to hold the text "Hello".

Kotlin

class Box(val item: T)

val intBox: Box = Box(123)
# Your code here

Need a hint?

Write val stringBox: Box<String> = Box("Hello") to create the string box.

4

Print the box contents

Print the contents of intBox and stringBox using println. Print intBox.item first, then stringBox.item.

Kotlin

class Box(val item: T)

val intBox: Box = Box(123)
val stringBox: Box = Box("Hello")
# Your code here

Need a hint?

Use println(intBox.item) and println(stringBox.item) to show the contents.