Kotlin Design Patterns and Best Practices/

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Command Design Pattern

Command Design Pattern

Learn how to implement the Command design pattern in Kotlin.

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The Command design pattern allows us to encapsulate actions inside an object to be executed sometime later. Furthermore, if we can execute one action later, we could also execute many, or even schedule exactly when to execute them.

Let’s once again imagine we want to build a system to manage different kinds of troopers for the Galactic Empire. Here’s an example of implementing the attack and move functions:

class Stormtrooper(...) {
    fun attack(x: Long, y: Long) {
          println("Attacking ($x, $y)")
          // Actual code here
    }
    fun move(x: Long, y: Long) {
        println("Moving to ($x, $y)")
       // Actual code here
    }
}
A class Stormtrooper with attack and move functions

The problem we need to solve now is that our trooper can remember exactly one command. That’s it. If they start at (0,0)(0, 0), which is the top of the screen, we can tell them to move (20,0)(20, 0), which is 2020 ...