Exercise: Implementing the Product class

Define the Product class with properties:

• name (String): The product's name.
• price (Double): The product's price.
• quantity (Int): The initial quantity of the product.

Implement a custom setter for the quantity property that ensures that negative values are set to zero.

Add a method named calculateTotalValue that returns the product's total value.

Implement a method named restock that increases the product's quantity by a specified positive amount. If a negative value is specified, the method should do nothing.

Instructions:

1. Define the Product class with primary constructor properties name, price, and parameter quantity.
2. Implement a property quantity with a custom setter.
3. Implement the calculateTotalValue method to calculate and return the total value.
4. Implement the restock method to increase the quantity.
5. Test your implementation by creating instances of the Product class and using its methods.

Example usage:

val laptop = Product("Laptop", 999.99, 5)

println(laptop.name) // Laptop
println(laptop.quantity) // 5
println(laptop.calculateTotalValue()) // 4999.95

laptop.restock(3)

println(laptop.quantity) // 8
println(laptop.calculateTotalValue()) // 7999.92

laptop.quantity = -2

println(laptop.quantity) // 0
println(laptop.calculateTotalValue()) // 0.0

laptop.quantity = 10

println(laptop.quantity) // 10
println(laptop.calculateTotalValue()) // 9999.9

This problem can either be solved in the below playground or you can clone kotlin-exercises project and solve it locally. In the project, you can find code template for this exercise in essentials/classes/Product.kt. You can find there example usage and unit tests.

Hints:

• Use the field keyword in the custom setter to modify the backing field.
• Calculate the total value by multiplying price and quantity.

Once you are done with the exercise, you can check your solution here.

Playground

import org.junit.Test
import kotlin.test.assertEquals

// TODO

fun main() {
    val laptop = Product("Laptop", 999.99, 5)
    
    println(laptop.name) // Laptop
    println(laptop.quantity) // 5
    println(laptop.calculateTotalValue()) // 4999.95
    
    laptop.restock(3)
    
    println(laptop.quantity) // 8
    println(laptop.calculateTotalValue()) // 7999.92
    
    laptop.quantity = -2
    
    println(laptop.quantity) // 0
    println(laptop.calculateTotalValue()) // 0.0
    
    laptop.quantity = 10
    
    println(laptop.quantity) // 10
    println(laptop.calculateTotalValue()) // 9999.9
}

class ProductTest {
   @Test
   fun `should keep name, price and quantity`() {
       val product = Product("Apple", 1.0, 10)
       assertEquals("Apple", product.name)
       assertEquals(1.0, product.price)
       assertEquals(10, product.quantity)
   }
 
   @Test
   fun `should calculate total value`() {
       assertEquals(10.0, Product("Apple", 1.0, 10).calculateTotalValue())
       assertEquals(0.0, Product("Apple", 1.0, 0).calculateTotalValue())
       assertEquals(0.0, Product("Apple", 0.0, 10).calculateTotalValue())
       assertEquals(4.8, Product("Apple", 1.2, 4).calculateTotalValue())
   }
 
   @Test
   fun `should restock`() {
       val product = Product("Apple", 1.0, 10)
       product.restock(5)
       assertEquals(15, product.quantity)
       product.restock(-5)
       assertEquals(15, product.quantity)
       product.restock(0)
       assertEquals(15, product.quantity)
   }
 
   @Test
   fun `should not allow negative quantity`() {
       val product = Product("Apple", 1.0, 10)
       product.quantity = -5
       assertEquals(0, product.quantity)
       product.quantity = 8
       assertEquals(8, product.quantity)
       product.quantity = 0
       assertEquals(0, product.quantity)
   }
}