Can you tell the differences between 1. sealed int...

# android

[chanjungskim]

Can you tell the differences between
1. sealed interface vs sealed class
2. sealed interface vs interface
And with examples?

[Javier]

classes can have state and interfaces can’t.

a sealed interface is closed in terms of you will know with pattern matching what are the implementations that exist. With a normal interface you can’t

[chanjungskim]

what is pattern matching?

[Tom Hermann]

An interface defines a contract that a class can implement. Here is an example from the java website converted to Kotlin:

package com.example

interface Bicycle {
    fun changeCadence(newValue: Int)
    fun changeGear(newValue: Int)
    fun speedUp(increment: Int)
    fun applyBrakes(decrement: Int)
}

Note that this interface simply defines what you can generally do with a bicycle, not how it is accomplished.

Classes can implement interfaces, so if you wanted to model a Peloton for example, you could start like this:

package com.example

class Peloton : Bicycle {
    override fun changeCadence(newValue: Int) {
        // perform change cadence
    }

    override fun changeGear(newValue: Int) {
        // perform change gear
    }

    override fun speedUp(increment: Int) {
        // perform speed up
    }

    override fun applyBrakes(decrement: Int) {
        // perform slow down
    }
}

In this example a Peloton is-a bicycle, since it implements the bicycle interface, so anywhere that wants a "bicycle" will accept a Peloton.

So lets say you have a "Rider" that can ride any old bicycle. Here is an example of creating a rider instance and having them ride a peloton.

package com.example

class Rider {
    fun ride(bicycle: Bicycle) {
        bicycle.changeGear(1)
        bicycle.speedUp(11)
    }
}

fun main() {
    val peloton = Peloton()
    Rider().ride(peloton)
}

So you can see that you could swap out different bike implementations (imagine a MountainBike, BmxBike , etc.)
and as long as it conforms to the contract you can have the rider ride it.

Once you fully understand classes / interfaces, Kotlin's site has a great write-up on sealed interfaces and classes:
https://kotlinlang.org/docs/sealed-classes.html