The Builder Pattern

July 9, 2018 Coding

What is this pattern for?

This pattern is used when it’s necessary to isolate the construction of a complex object and at the same time have more than one representation.

Featuring:

The Client:

They want an application with a specific construction. In this case, they want an application written in Kotlin.

The Director:

This person knows the application parts and the requisites from the client, but he or she doesn’t know how to do it.

The Developers:

The team follows the Director’s indications to deliver an application to the Client. Each of them has a specific technical knowledge, in this case, a programming language.

The model:

The code:

class Director(val developer: Developer){
    fun orderCreateApplication() {
        developer.createDatabase()
        developer.createBackend()
        developer.createUserInterface()
    }
}

open class Developer {
    open fun createDatabase() {}
    open fun createBackend() {}
    open fun createUserInterface() {}
    open fun deliverApplication(): String? { return null}
}

class JavaDeveloper(): Developer() {
    override fun createBackend() {
        println("[Java developer] Backend created!")
    }
    override fun createUserInterface() {
        println("[Java developer] User Interface created!")
    }
    override fun createDatabase() {
        println("[Java developer] Database created!")
    }
    override fun deliverApplication(): String {
        return "Here you go! Your Java Application."
    }
}

class KotlinDeveloper : Developer() {
    override fun createBackend() {
        println("[Kotlin developer] Backend created!")
    }
    override fun createUserInterface() {
        println("[Kotlin developer] User Interface created!")
    }
    override fun createDatabase() {
        println("[Kotlin developer] Database created!")
    }
    override fun deliverApplication(): String {
        return "Here you go! Your Kotlin Application."
    }
}

class ScalaDeveloper : Developer() {
    override fun createBackend() {
        println("[Scala developer] Backend created!")
    }
    override fun createUserInterface() {
        println("[Scala developer] User Interface created!")
    }
    override fun createDatabase() {
        println("[Scala developer] Database created!")
    }
    override fun deliverApplication(): String {
        return "Here you go! Your Scala Application."
    }
}

The pattern in action:

The Sequence Diagram:

The code:

fun main(args: Array<String>) {
    // The client wants an application written in Kotlin
    val circleTheDeveloper = KotlinDeveloper()
    // The director instructs the developer with client's requisites
    val pentagonTheDirector = Director(squareTheDeveloper)
    pentagonTheDirector.orderCreateApplication()
    // The developer delivers the result
    val applicationResult = squareTheDeveloper.deliverApplication()
    println(applicationResult)
}

[Kotlin developer] Database created!
[Kotlin developer] Backend created!
[Kotlin developer] User Interface created!
Here you go! Your Kotlin Application.

Process finished with exit code 0

Source

Tags: