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Strategy Pattern

In the Strategy pattern, a class behavior or its algorithm can be changed at run time. This type of design pattern comes under behavior pattern.

In the Strategy pattern, we create objects which represent various strategies and a context object whose behavior varies as per its strategy object. The strategy object changes the executing algorithm of the context object.

class Printer(val strategy: (String) -> String) {
    fun print(string: String): String = strategy(string)
}
val lowerCaseFormatter: (String) -> String = String::toLowerCase
val upperCaseFormatter: (String) -> String = String::toUpperCase
fun main(args: Array<String>) {
    val lower = Printer(strategy = lowerCaseFormatter)
    println(lower.print("O tempora, o mores!"))
    val upper = Printer(strategy = upperCaseFormatter)
    println(upper.print("O tempora, o mores!"))
}

The output of kotlin strategy pattern

o tempora, o mores!
O TEMPORA, O MORES!


Another Example for kotlin Strategy Design Pattern

interface BookingStrategy {
    val fare: Double
}

class CarBookingStrategy : BookingStrategy {

    override val fare: Double = 12.5

    override fun toString(): String {
        return "CarBookingStrategy"
    }
}

class TrainBookingStrategy : BookingStrategy {

    override val fare: Double = 8.5

    override fun toString(): String {
        return "TrainBookingStrategy"
    }
}

class Customer(var bookingStrategy: BookingStrategy) {

    fun calculateFare(numOfPassangeres: Int): Double {
        val fare = numOfPassangeres * bookingStrategy.fare
        println("Calculating fares using " + bookingStrategy)
        return fare
    }
}

fun main(args: Array<String>) {

    //CarBooking Strategy
    val cust = Customer(CarBookingStrategy())
    var fare = cust.calculateFare(5)
    println(fare)

    //TrainBooking Strategy
    cust.bookingStrategy = TrainBookingStrategy()
    fare = cust.calculateFare(5)
    println(fare)
}

The output of kotlin strategy pattern

Calculating fares using CarBookingStrategy
62.5
Calculating fares using TrainBookingStrategy
42.5
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