Careeroza

Real World Example

Ride Types in a Ride-hailing App

Uber, Ola and Rapido offer several ride types that share most logic (base fare, distance) but differ in pricing rules. A parent class holds the common code and each ride type overrides only what changes.

Example

open class Ride(val distanceKm: Double) {
    open val name = "Ride"
    open val baseFare = 30.0
    open val perKm = 10.0

    open fun fare(): Double = baseFare + distanceKm * perKm

    fun receipt() = println("%-8s %5.1f km  Rs %.0f".format(name, distanceKm, fare()))
}

class BikeRide(d: Double) : Ride(d) {
    override val name = "Bike"
    override val baseFare = 15.0
    override val perKm = 6.0
}

class AutoRide(d: Double) : Ride(d) {
    override val name = "Auto"
    override val perKm = 12.0
}

class PremiumRide(d: Double, val surge: Double) : Ride(d) {
    override val name = "Premier"
    override val baseFare = 80.0
    override val perKm = 18.0
    override fun fare() = super.fare() * surge   // reuse parent logic
}

fun main() {
    val options = listOf(BikeRide(8.0), AutoRide(8.0), Ride(8.0), PremiumRide(8.0, 1.25))
    options.forEach { it.receipt() }
}

Output

Bike       8.0 km  Rs 63
Auto       8.0 km  Rs 126
Ride       8.0 km  Rs 110
Premier    8.0 km  Rs 280

Android: a Base Activity

Many Android projects have a base class with shared behaviour (analytics, loading dialog). Every screen extends it and calls super in lifecycle methods.

abstract class BaseActivity : AppCompatActivity() {
    abstract val screenName: String

    override fun onResume() {
        super.onResume()                       // always call the framework version
        Analytics.logScreen(screenName)
    }

    protected fun showError(message: String) {
        Snackbar.make(findViewById(android.R.id.content), message, Snackbar.LENGTH_LONG).show()
    }
}

class CheckoutActivity : BaseActivity() {
    override val screenName = "checkout"
}

Tip: Prefer composition over deep inheritance trees. One or two levels is fine; five levels of base classes become hard to change.