Какие знаешь реализации паттернов

### Singleton ```java public class Singleton { private static Singleton instance; private Singleton() {} public static synchronized Singleton getInstance() { if (instance == null) { instance = new Singleton(); } return instance; } } ``` Или через enum (рекомендуемый способ): ```java public enum Singleton { INSTANCE; } ``` ### Factory Method ```java interface Product {} class ConcreteProductA implements Product {} class ConcreteProductB implements Product {} abstract class Creator { abstract Product createProduct(); } class ConcreteCreatorA extends Creator { Product createProduct() { return new ConcreteProductA(); } } ``` ### Observer ```java interface Observer { void update(String message); } class ConcreteObserver implements Observer { public void update(String message) { System.out.println("Received: " + message); } } class Subject { private List observers = new ArrayList<>(); public void addObserver(Observer o) { observers.add(o); } public void notifyObservers(String message) { observers.forEach(o -> o.update(message)); } } ``` ### Decorator ```java interface Component { void operation(); } class ConcreteComponent implements Component { public void operation() { System.out.println("Basic operation"); } } class Decorator implements Component { private Component component; public Decorator(Component c) { this.component = c; } public void operation() { component.operation(); System.out.println("Decorator operation"); } } ``` ### Strategy ```java interface Strategy { void execute(); } class ConcreteStrategyA implements Strategy { public void execute() { System.out.println("Strategy A"); } } class Context { private Strategy strategy; public void setStrategy(Strategy s) { this.strategy = s; } public void executeStrategy() { strategy.execute(); } } ```