Kotlin Koans—Part 17

This part of Kotlin Koans continues to build on the features Kotlin offers on collection. Most of these methods will look familiar to people who have worked with Java 8 streams.

In this portion of the tutorial, I had to work with the maxBy method. It’s a nice little shortcut method to find an item based on a property. There is also a companion minBy.

fun Shop.getCustomerWithMaximumNumberOfOrders(): Customer? {
    // Return a customer whose order count is the highest among all customers
    return customers.maxBy { it.orders.size }
}

fun Customer.getMostExpensiveOrderedProduct(): Product? {
    // Return the most expensive product which has been ordered
    return orderedProducts.maxBy { it.price }
}

I was curious about what it would take to solve this problem in Java. Here is what I came up with.

public static Optional getCustomerWithMaximumNumberOfOrders(Shop shop){
    return shop.getCustomers().stream().max(Comparator.comparingInt(lhs -> lhs.getOrders().size()));
}

I can’t say it was too brutal, but I think maxBy is much easier to read and understand as opposed to stream().max(Comparator.comparingInt(lhs -> lhs.getOrders().size()))

You can click here to see Part 16