Kotlin Design Patterns — The Command

Just a quick intro to the Command Pattern in Kotlin. And a comparison to it’s Java counterpart.

Kotlin

*_*

Java

Oh the verbosity! :|

Output

The code difference between Kotlin & Java is quite significant here. I had to unwrap a few lines just so I could have the code on one page.

Let’s go over the components

OrderCommand: An interface with just an apply/execute method

AddOrderCommand & PayOrderCommand: Two classes implementing the same OrderCommand interface

OrdersCommandProcessor: Manages & executes the commands

Kotlin has apply block, which is an inline function — in simple terms, it recieves this and returns this. Without the apply block, the code would’ve looked very similar to the Java code.

Happy Coding!

Example taken from: Design Patterns in Kotlin

Previous Pattern: The Strategy