Factory

• Loose coupling
• OC principle
• default in interface

🛠️ When to use factory

• When you want to create several types of smth with different values
• give the creation role to a factory
• 👀 You have class Circle and Square extending Interface Shape
• you want to create Circle or Square using one constructor
• 👀 You have class WhiteShip and BlackShip extending Ship
• you want to create WhiteShip and BlackShip just with one method, without using else-if for checking the names and settings colors…

✅ Factory Pattern

• factory안에서 구체적인 클래스를 만들어낸다
• ⭐️ Loosely coupled: make coupling between class and constructor loose
• <<Interface>> will be responsible for constructing a class
• delegate object creation to a factory
• ⭐️ Open/Closed principle: open to extension, closed to modification

👎🏻 If there was no factory pattern

• ✔️ Class Ship

public class Ship {
    private String name;
    private String color;
    private String logo;

  //getters
  //setters
}

• ✔️ Class ShipFactory
• 👎🏻 need to check name and set logo and color accordingly

        // Customizing for specific name
        if (name.equalsIgnoreCase("whiteship")) {
            ship.setLogo("\uD83D\uDEE5️");
        } else if (name.equalsIgnoreCase("blackship")) {
            ship.setLogo("⚓");
        }

        // coloring
        if (name.equalsIgnoreCase("whiteship")) {
            ship.setColor("whiteship");
        } else if (name.equalsIgnoreCase("blackship")) {
            ship.setColor("black");
        }

✅ After factory pattern

• ✔️ Class Ship

public class Ship {
    private String name;
    private String color;
    private String logo;

  //getters
  //setters
}

• ✔️ Class WhiteShip and BlackShip
• ⭐️ How to set attributes of parent without using constructor

public class WhiteShip extends Ship {
    public WhiteShip() {
        setName("White Ship");
        setLogo("aaa");
        setColor("white");
    }
}

public class BlackShip extends Ship{
    public BlackShip() {
        setName("BlackShip");
        setLogo("bbbb");
        setColor("black");
    }
}

• ✔️ Interface ShipFactory

public interface ShipFactory {
  //default, could/could not be overrided
    default Ship orderShip(String name, String email){
        validate(name, email);
        Ship ship = createShip(); //use createShip();
        sendEmailTo(email, ship);
        return ship;
    }

    Ship createShip(); //not defined, must be overrided

}

• validate(), sendEmailTo() are methods I want to run as soon as I create Ship

• ✔️ Class WhiteShipFactory and BlackShipFactory

public class WhiteShipFactory implements ShipFactory{
    @Override
    public Ship createShip() {
        return new WhiteShip();
    }
}

public class BlackShipFactory implements ShipFactory{
    @Override
    public Ship createShip() {
        return new BlackShip();
    }
}

• ✔️ CLient code

public class Client {
    public static void main(String[] args) {
        Ship whiteShip = new WhiteShipFactory().orderShip("WhiteShip", "aaa@gmail.com");
        Ship blackShip = new BlackShipFactory().orderShip("BlackShip", "bbb@gmail.com");
    }
}

👍🏻 Advantages 👎🏻 Disadvantages

• 👍🏻 do not need to use else-if
• 👍🏻 open/closed principle: open for extension, closed for modification
  • can create another function/interface without modifying the old code
  • this is bc of coupling between class and constructor is loose

• 👍🏻 can use default to write a default method in interface

• 👎🏻 need to create more classes

default and private in interface

• can use default to define a method in interface
• and the helper methods for the default method should be private
• as it would be used only inside the interface

public interface ShipFactory {
    default Ship orderShip(String name, String email){
        validate(name, email);
        prepareFor(name);
        Ship ship = createShip();
        sendEmailTo(email, ship);
        return ship;
    }

  //helper methods inside default method
  //access modifier: private
  private void validate(String name, String email){

    }

    private void prepareFor(String name) {

    }