patterns2FactoryMethodPattern

1package pkg8patterns;2 3/*4 * Factory Method (Creational)5 * ---------------------------6 * INTENT: define an interface for creating an object, but let subclasses decide7 *         which class to instantiate.8 * UML: Creator + factoryMethod(): Product ; ConcreteCreator overrides it.9 * PROS: decouples client from concrete classes; open/closed for new products.10 * CONS: many small subclasses.11 * REAL-WORLD: java.util.Calendar.getInstance, NumberFormat.getInstance.12 */13public class patterns2FactoryMethodPattern {14 15    interface Notification { String send(); }16    static class Email implements Notification { public String send() { return "Email sent"; } }17    static class Sms implements Notification { public String send() { return "SMS sent"; } }18    static class Push implements Notification { public String send() { return "Push sent"; } }19 20    // Factory method centralizes object creation21    static Notification create(String type) {22        return switch (type.toLowerCase()) {23            case "email" -> new Email();24            case "sms"   -> new Sms();25            case "push"  -> new Push();26            default -> throw new IllegalArgumentException("unknown type: " + type);27        };28    }29 30    public static void main(String[] args) {31        for (String t : new String[]{"email", "sms", "push"}) {32            System.out.println(t + " -> " + create(t).send());33        }34    }35}