Strategy pattern example using kotlin scripts

I thought it would be nice to use advantages of Kotlin language to showcase strategy pattern implementation. In order to get the example running – we need to install kotlin binaries (installation). I’m running simple Kotlin script in this example.

Having scripting support it makes it very easy to fire up some process with full Kotlin language capabilities. You could use it to do some kind of administrative tasks in your business environment.

tip

Using Kotlin scripts there's no need for main method, you just write code to execute directly (there's a args variable available so that one can access command line arguments passed)

note

make sure to have kotlinc on your \$PATH

Strategy pattern example

As stated on the Wikipedia:

In computer programming, the strategy pattern (also known as the policy pattern) is a behavioral software design pattern that enables selecting an algorithm at runtime. Instead of implementing a single algorithm directly, code receives run-time instructions as to which in a family of algorithms to use

Our example will demonstrate just that - we'll call our application providing some command line argument. Based on passed argument value, we'll pick on of available application strategies to build the town: slow, medium or fast - different ways to build one town.

class TownBuilder {
        private val slow = { -> 3000L }
        private val medium = { -> 1500L }
        private val fast = { -> 50L }
        val buildingStrategy: () -> Long

        init {
            buildingStrategy = when (args[0]) {
                "slow" -> slow
                "medium" -> medium
                "fast" -> fast
                else -> throw IllegalArgumentException("Invalid speed")
            }
        }

        fun build() {
            val pace = buildingStrategy.invoke()
            Thread.sleep(pace)
            println("Town built in $pace milliseconds!")
        }
    }
    TownBuilder().build()

As we can see the TownBuilder decides which town building strategy to use based in input command line argument. The strategy is, basically, just a function that returns how much the thread should sleep (emulating long process of building one town).

Running the app

• Without unsupported command line arguments

$ kotlinc -script strategy.kts 200
java.lang.IllegalArgumentException: Invalid speed
        at Strategy.<init>(strategy.kts:9)

• Slow pace town building

$ kotlinc -script strategy.kts slow

Building at slow pace...

Town built in 3000 milliseconds!

• Medium pace town building

kotlinc -script strategy.kts medium

Building at medium pace...

Town built in 1500 milliseconds!

• Fast pace town building

kotlinc -script strategy.kts fast

Building at fast pace...

Town built in 50 milliseconds!

Original Source Code can be found on GitHub as a Gist.

That was all for today! Hope you liked it!