Kotlin - Design Pattern In Easy Way | Creational Patterns

01-builderdemo.java

class Car {

    String type;
    String model;
    String color;
    int speed;

    Car(String type, String model, String color) {
        this.type = type;
        this.model = model;
        this.color = color;
    }

    @Override
    public String toString() {
        return "Car{" +
                "type='" + type + '\'' +
                ", model='" + model + '\'' +
                ", color='" + color + '\'' +
                ", speed=" + speed +
                '}';
    }
}

public class BuilderDemo {
    public static void main(String args[]) {
        List<Car> cars = Arrays.asList(
                new Car("Ford", "Focus", "red"),
                new Car("Toyota", "Auris", "blue"),
                new Car("Volkswagen", "Golf", "green")
        );
        cars.forEach(System.out::println);
    }
}

02-builderdemo.java

import java.util.Arrays;
import java.util.List;

class Car {

    String type;
    String model;
    String color;
    int speed = 10; // Default speed

    Car(String type, String model, String color, int speed) {
        this.type = type;
        this.model = model;
        this.color = color;
        this.speed = speed;
    }
    Car(String type, String model, String color) {
        this.type = type;
        this.model = model;
        this.color = color;
    }

    Car(String type, String model) {
        this.type = type;
        this.model = model;
        this.color = "black"; // Default color in constructor
    }

    // rest of the code 
}

public class BuilderDemo {
    public static void main(String args[]) {
        List<Car> cars = Arrays.asList(
                new Car("Ford", "Focus", "red", 100),
                new Car("Toyota", "Auris", "blue"),
                new Car("Volkswagen", "Golf")
        );
        cars.forEach(System.out::println);
    }
}

03-builderdemo.java

import java.util.Arrays;
import java.util.List;

class Car {

    private final String type;
    private final String model;
    private String color;
    private int speed;

    Car(String type, String model, String color, int speed) {
        this.type = type;
        this.model = model;
        this.color = color;
        this.speed = speed;
    }

    // Define getters only

    @Override
    public String toString() {
        return "Car{" +
                "type='" + type + '\'' +
                ", model='" + model + '\'' +
                ", color='" + color + '\'' +
                ", speed=" + speed +
                '}';
    }

    public static class CarBuilder {
        private final String type;
        private final String model;
        private String color;
        private int speed;

        public CarBuilder(String type, String model) {
            this.type = type;
            this.model = model;
        }

        public CarBuilder color(String color) {
            this.color = color;
            return this;
        }

        public CarBuilder speed(int speed) {
            this.speed = speed;
            return this;
        }

        public Car build() {
            Car car = new Car(this.type, this.model, this.color, this.speed);
            this.setDefaults(car);
            return car;
        }

        private void setDefaults(Car car) {
            if (car.speed == 0) {
                car.speed = 10;
            }
            if (car.color == null) {
                car.color = "black";
            }
        }
    }
}

public class BuilderDemo {
    public static void main(String[] args) {
        Car fordCar = new Car.CarBuilder("Ford", "Focus").speed(100).color("red").build();
        Car toyotaCar = new Car.CarBuilder("Toyota", "Auris").color("blue").build();
        Car volksCar = new Car.CarBuilder("Volkswagen", "Golf").build();
        List<Car> cars = Arrays.asList(
                fordCar,
                toyotaCar,
                volksCar
        );
        cars.forEach(System.out::println);
    }
}

04-builderdemo.kt

class CarKt(
    private val type: String,
    private val model: String,
    private val color: String = "black", // default color
    private val speed: Int = 10 // Default Speed
){
    override fun toString(): String {
        return "CarKt(type='$type', model='$model', color='$color', speed=$speed)"
    }
}

fun main(args: Array<String>) {
    val fordCar = CarKt("Ford", "Focus", "red", 100)
    val toyotaCar = CarKt("Toyota", "Auris", "blue")
    val volksCar = CarKt("Volkswagen", "Golf")
    val cars = listOf(
        fordCar,
        toyotaCar,
        volksCar
    )
    cars.forEach { x -> println(x) }
}

05-builderdemo.kt

// rest of the code

fun main(args: Array<String>) {
    val fordCar = CarKt("Ford", "Focus", "red", 100)
    val toyotaCar = CarKt("Toyota", "Auris", speed = 120)
    val volksCar = CarKt("Volkswagen", "Golf")
    val cars = listOf(
        fordCar,
        toyotaCar,
        volksCar
    )
    cars.forEach { x -> println(x) }
    /*
    CarKt(type='Ford', model='Focus', color='red', speed=100)
    CarKt(type='Toyota', model='Auris', color='black', speed=120)
    CarKt(type='Volkswagen', model='Golf', color='black', speed=10)
    */
}

06-single.java

class LazySingleton {
    private static volatile LazySingleton instance = null;

    // private constructor
    private LazySingleton() {
    }

    public static LazySingleton getInstance() {
        if (instance == null) {
            synchronized (LazySingleton.class) {
                // Double check
                if (instance == null) {
                    instance = new LazySingleton();
                }
            }
        }
        return instance;
    }
}

077-single.kt

package singleton

class LazySingletonKt {
    companion object {
        @Volatile
        private var instance: LazySingletonKt? = null
        fun get(): LazySingletonKt? {
            if (instance == null) {
                synchronized(LazySingletonKt::class.java) {
                    if (instance == null) {
                        instance = LazySingletonKt()
                    }
                }
            }
            return instance
        }
    }
}

fun main() {
    val lazySingletonKt1 = LazySingletonKt.get();
    val lazySingletonKt2 = LazySingletonKt.get();
    println(lazySingletonKt1 == lazySingletonKt2) // true
}

08-single.kt

object SingletonObjectKt {
    var id: Int = 0;
    fun getId() = this.toString()
}

fun main() {
    val lazySingletonKt1 = SingletonObjectKt;
    lazySingletonKt1.id = 1;
    val lazySingletonKt2 = SingletonObjectKt;
    println(lazySingletonKt1.id == lazySingletonKt2.id)
    println(lazySingletonKt1.id)
    println(lazySingletonKt1.getId() == lazySingletonKt2.getId())
    println(lazySingletonKt1.getId())
}

09-factory.java

enum CarType {
    SMALL, LUXURY
}

abstract class Car {
    private CarType model = null;
    public Car(CarType model) {
        this.model = model;
    }

    protected abstract void construct();
}

class LuxuryCar extends Car {

    LuxuryCar() {
        super(CarType.LUXURY);
        construct();
    }

    @Override
    protected void construct() {
        System.out.println("Building luxury car");
    }
}
class SmallCar extends Car {
    SmallCar() {
        super(CarType.SMALL);
        construct();
    }

    @Override
    protected void construct() {
        System.out.println("Building small car");
    }
}
class CarFactory {
    public static Car buildCar(CarType model) {
        Car car = null;
        switch (model) {
            case LUXURY:
                car = new LuxuryCar();
                break;
            default:
                car = new SmallCar();
                break;
        }
        return car;
    }
}
public class FactoryDemo {
    public static void main(String[] args) {
        System.out.println(CarFactory.buildCar(CarType.SMALL));
        System.out.println(CarFactory.buildCar(CarType.LUXURY));
    }
}

10-factory.kt

enum class CarTypeKt {
    SMALL, LUXURY
}

abstract class CarKt(val model: CarTypeKt) {
    protected abstract fun construct()
}

class LuxuryCarKt : CarKt(CarTypeKt.LUXURY) {
    override fun construct() {
        println("Building luxury car")
    }

    init {
        construct()
    }
}

class SmallCarKt : CarKt(CarTypeKt.SMALL) {
    override fun construct() {
        println("Building small car")
    }

    init {
        construct()
    }
}

object CarFactoryKt {
    fun buildCar(model: CarTypeKt = CarTypeKt.SMALL) = when (model) {
        CarTypeKt.LUXURY -> LuxuryCarKt()
        else -> SmallCarKt()
    }
}

fun main() {
    println(CarFactoryKt.buildCar(CarTypeKt.LUXURY).model)
    println(CarFactoryKt.buildCar().model)
}